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Mass in ahler Geometry Claude LeBrun Stony Brook University New Horizons in Twistor Theory Oxford, January 5, 2017
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Page 1: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Mass in

Kahler Geometry

Claude LeBrunStony Brook University

New Horizons in Twistor TheoryOxford, January 5, 2017

1

Page 2: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Joint work with

2

Page 3: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Joint work with

Hans-Joachim HeinUniversity of Maryland

3

Page 4: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Joint work with

Hans-Joachim HeinFordham University

4

Page 5: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Joint work with

Hans-Joachim HeinFordham University

Comm. Math. Phys. 347 (2016) 621–653.

5

Page 6: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn

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Page 7: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn

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Page 8: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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n ≥ 3

8

Page 9: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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Page 10: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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Page 11: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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11

Page 12: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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12

Page 13: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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~x

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gjk,` = O(|x|−n2−ε), s ∈ L1

13

Page 14: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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~x

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gjk,` = O(|x|−n2−ε), s ∈ L1

14

Page 15: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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~x

gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), scalar curvature ∈ L1

15

Page 16: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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~x

gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

16

Page 17: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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~x

gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

17

Page 18: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

18

Page 19: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

19

Page 20: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

20

Page 21: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

21

Page 22: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each component of M − K is diffeo-morphic to Rn −Dn in such a manner that

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gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

22

Page 23: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. A complete, non-compact Rieman-nian n-manifold (Mn, g) is called asymptoticallyEuclidean (AE) if there is a compact set K ⊂Msuch that each “end” component of is diffeo-morphic to Rn −Dn in such a manner that

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gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

23

Page 24: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(R

n −Dn)/Γi, where Γi ⊂ O(n), such that

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24

Page 25: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(R

n −Dn)/Γi, where Γi ⊂ O(n), such that

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25

Page 26: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(R

n −Dn)/Γi, where Γi ⊂ O(n), such that

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26

Page 27: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(Rn −Dn)/Γi, where Γi ⊂ O(n), such that

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27

Page 28: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(Rn −Dn)/Γi, where Γi ⊂ O(n), such that

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28

Page 29: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(Rn −Dn)/Γi, where Γi ⊂ O(n), such that

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29

Page 30: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(Rn −Dn)/Γi, where Γi ⊂ O(n), such that

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30

Page 31: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(Rn −Dn)/Γi, where Γi ⊂ O(n), such that

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....

gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

31

Page 32: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Why consider ALE spaces?

32

Page 33: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

33

Page 34: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

34

Page 35: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

35

Page 36: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

By contrast, any Ricci-flat AE manifold must beflat, by the Bishop-Gromov inequality. . .

36

Page 37: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

37

Page 38: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

Γ ∼= Z` ⊂ SU(2) ⊂ O(4).

38

Page 39: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

vv

vvv

Data: ` points in R3. =⇒ V with ∆V = 0

39

Page 40: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

vv

vvv

Data: ` points in R3. =⇒ V with ∆V = 0

V =∑j=1

1

2%j

40

Page 41: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

vv

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Data: ` points in R3. =⇒ V with ∆V = 0

V =∑j=1

1

2%j

F = ?dV curvature θ on P → R3 − pts.

41

Page 42: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

vv

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Data: ` points in R3. =⇒ V with ∆V = 0

g = V h + V −1θ2

F = ?dV curvature θ on P → R3 − pts.

42

Page 43: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

vv

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Data: ` points in R3. =⇒ V with ∆V = 0

g = V h + V −1θ2

on P . Then take M4 = Riemannian completion.

43

Page 44: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

Γ ∼= Z` ⊂ SU(2) ⊂ O(4).

44

Page 45: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

Γ ∼= Z` ⊂ SU(2) ⊂ O(4).

The G-H metrics are hyper-Kahler, and were soonrediscovered independently by Hitchin.

45

Page 46: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

46

Page 47: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................

47

Page 48: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................

48

Page 49: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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49

Page 50: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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50

Page 51: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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51

Page 52: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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52

Page 53: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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53

Page 54: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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54

Page 55: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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55

Page 56: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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56

Page 57: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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57

Page 58: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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58

Page 59: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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59

Page 60: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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60

Page 61: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Kahler metrics:

(Mn, g): Kahler ⇐⇒ holonomy ⊂ U(m)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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61

Page 62: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ Sp(1)

s

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62

Page 63: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ Sp(1)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................

Sp(1) = SU(2)

63

Page 64: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ Sp(1)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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Sp(1) = SU(2)

⇐⇒ Λ+ flat and trivial.

64

Page 65: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ Sp(1)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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Sp(1) = SU(2)

⇐⇒ Λ+ flat and trivial.

Locally, ⇐⇒ s = 0, r = 0, W+ = 0.

65

Page 66: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ Sp(1)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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Sp(1) = SU(2)

Ricci-flat and Kahler,

for many different complex structures!

66

Page 67: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ U(2)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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Sp(1) ⊂ U(2)

Ricci-flat and Kahler,

for many different complex structures!

67

Page 68: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ Sp(1)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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Sp(1) = SU(2)

Ricci-flat and Kahler,

for many different complex structures!

68

Page 69: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

All these complex structures can be repackaged as

Penrose Twistor Space (Z6, J),

which is a complex 3-manifold

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69

Page 70: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

All these complex structures can be repackaged as

Penrose Twistor Space (Z, J),

which is a complex 3-manifold

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70

Page 71: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

All these complex structures can be repackaged as

Penrose Twistor Space (Z, J),

which is a complex 3-manifold.

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71

Page 72: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

All these complex structures can be repackaged as

Penrose Twistor Space (Z, J),

which is a complex 3-manifold.

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Riemannian non-linear graviton construction.

72

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Hitchin’s Twistor Spaces:

73

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3⊃ R3.

74

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3 ⊃ R3.

75

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3 ⊃ R3.

vv

vvv

So ` points determine P1, . . . , P` ∈ H0(CP1,O(2)).

76

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3 ⊃ R3.

vv

vvv

So ` points determine P1, . . . , P` ∈ H0(CP1,O(2)).

Small resolution Z of Z ⊂ O(`)⊕O(`)⊕O(2)

77

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3 ⊃ R3.

vv

vvv

So ` points determine P1, . . . , P` ∈ H0(CP1,O(2)).

Small resolution Z of Z ⊂ O(`)⊕O(`)⊕O(2)

xy = (z − P1) · · · (z − P`)

78

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3 ⊃ R3.

vv

vvv

So ` points determine P1, . . . , P` ∈ H0(CP1,O(2)).

Small resolution Z of Z ⊂ O(`)⊕O(`)⊕O(2)

xy = (z − P1) · · · (z − P`)

79

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Hitchin’s Twistor Spaces:

H0(CP1,O(2)) = C3 ⊃ R3.

vv

vvv

So ` points determine P1, . . . , P` ∈ H0(CP1,O(2)).

Small resolution Z of Z ⊂ O(`)⊕O(`)⊕O(2)

xy = (z − P1) · · · (z − P`)is the twistor space of a Gibbons-Hawking metric.

80

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Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

Γ ∼= Z` ⊂ SU(2) ⊂ O(4).

The G-H metrics are hyper-Kahler, and were soonrediscovered independently by Hitchin.

81

Page 82: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

Γ ∼= Z` ⊂ SU(2) ⊂ O(4).

The G-H metrics are hyper-Kahler, and were soonrediscovered independently by Hitchin.

Hitchin conjectured that similar metrics would existfor each finite Γ ⊂ SU(2).

82

Page 83: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Key examples:

Term ALE coined by Gibbons & Hawking, 1979.

They wrote down various explicit Ricci-flat ALE4-manifolds they called gravitational instantons.

Their examples have just one end, with

Γ ∼= Z` ⊂ SU(2) ⊂ O(4).

The G-H metrics are hyper-Kahler, and were soonrediscovered independently by Hitchin.

Hitchin conjectured that similar metrics would existfor each finite Γ ⊂ SU(2).

This conjecture was proved by Kronheimer, 1986.

83

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Felix Klein, 1884: C2/Γ → C3

Zk+1 ←→ xy + zk+1 = 0

Dih∗k−2 ←→ x2 + z(y2 + zk−2) = 0

T ∗ ←→ x2 + y3 + z4 = 0

O∗ ←→ x2 + y3 + yz3 = 0

I∗ ←→ x2 + y3 + z5 = 0

84

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Zk+1←→Ak • • • •.......................................................................................................................................................

Dih∗k−2←→Dk • • • ••.................................................................................................................

................................................

...........................................................

T ∗←→E6 • • • •••................................................................................................................................................................................................................

.......

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.......

....

O∗←→E7 • • • ••• •..................................................................................................................................................................................................................................................................

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....

I∗←→E8 • • • ••• • •....................................................................................................................................................................................................................................................................................................................

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.......

.......

.......

....

85

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Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ U(2)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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86

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Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ U(2)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

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................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................

In real dimension 4, any Kahler manifold satisfies

|W+|2 =s2

24

87

Page 88: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Hyper-Kahler metrics:

(M4, g) hyper-Kahler ⇐⇒ holonomy ⊂ U(2)

s

...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ .................................................................................................................................................................................

In real dimension 4, any Kahler manifold satisfies

|W+|2 =s2

24

so that W+ = 0 ⇐⇒ s = 0.

88

Page 89: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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89

Page 90: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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Kahler case: holomorphic section of KZ−1/2

vanishing at D := (M,J) ∩ (M,−J).

90

Page 91: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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rr Z

M 4

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Kahler case: holomorphic section of KZ−1/2

vanishing at D := (M,J) ∩ (M,−J).

=⇒ Normal bundle of (M,J) in Z is KM−1.

91

Page 92: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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0→ T 1,0M → T 1,0Z|M → KM−1→ 0

=⇒ Normal bundle of (M,J) in Z is KM−1.

92

Page 93: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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0→ T 1,0M → T 1,0Z|M → KM−1→ 0

Extension class: [ω] ∈ H1(M,O(KM⊗T 1,0M)).

93

Page 94: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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0→ T 1,0M → T 1,0Z|M → KM−1→ 0

Extension class: [ω] ∈ H1(M,Ω1).

94

Page 95: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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0→ T 1,0M → T 1,0Z|M → KM−1→ 0

Extension class: [ω] ∈ H1(M,Ω1).

95

Page 96: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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0→ T 1,0M → T 1,0Z|M → KM−1→ 0

Kahler class: [ω] ∈ H1(M,Ω1).

96

Page 97: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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rr Z

M 4

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0→ T 1,0M → T 1,0Z|M → KM−1→ 0

Kahler form: ω = g(J ·, ·).

97

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Some AE/ALE Scalar-Flat Kahler Surfaces:

98

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Some AE/ALE Scalar-Flat Kahler Surfaces:

(L ’91)

99

Page 100: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Some AE/ALE Scalar-Flat Kahler Surfaces:

100

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Some AE/ALE Scalar-Flat Kahler Surfaces:

f

vv

vvv

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.............

Data: k + 1 points in H3. =⇒ V with ∆V = 0

101

Page 102: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Some AE/ALE Scalar-Flat Kahler Surfaces:

f

vv

vvv

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.............

Data: k + 1 points in H3. =⇒ V with ∆V = 0

V = 1 +`

e2%0 − 1+

k∑j=1

1

e2%j − 1

102

Page 103: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Some AE/ALE Scalar-Flat Kahler Surfaces:

f

vv

vvv

.......

........................................

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.............

Data: k + 1 points in H3. =⇒ V with ∆V = 0

F = ?dV curvature θ on P → H3 − pts.

103

Page 104: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Some AE/ALE Scalar-Flat Kahler Surfaces:

f

vv

vvv

.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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.............

Data: k + 1 points in H3. =⇒ V with ∆V = 0

g =1

4 sinh2 %0

(V h + V −1θ2

)

104

Page 105: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Some AE/ALE Scalar-Flat Kahler Surfaces:

f

vv

vvv

.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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.............

Riemannian completion is ALE scalar-flat Kahler.

g =1

4 sinh2 %0

(V h + V −1θ2

)

105

Page 106: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Some AE/ALE Scalar-Flat Kahler Surfaces:

f

vv

vvv

.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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.............

Riemannian completion is AE ⇐⇒ ` = 1:

V = 1 +`

e2%0 − 1+

k∑j=1

1

e2%j − 1

106

Page 107: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4⊃ R1,3 ⊃ H3

107

Page 108: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3⊃ H3

108

Page 109: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

109

Page 110: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

f

vv

vvv

.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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.............

So k + 1 points in H3 give rise to

110

Page 111: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

f

vv

vvv

.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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.............

So k + 1 points in H3 give rise to

P0, P1, . . . , Pk ∈ H0(CP1 × CP1,O(1, 1)).

111

Page 112: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

112

Page 113: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

InO(k + `− 1, 1)⊕O(1, k + `− 1)→ CP1×CP1,

113

Page 114: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

InO(k + `− 1, 1)⊕O(1, k + `− 1)→ CP1×CP1,

let Z be the hypersurface

xy = P `0 P1 · · · Pk.

114

Page 115: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

InO(k + `− 1, 1)⊕O(1, k + `− 1)→ CP1×CP1,

let Z be the hypersurface

xy = P `0 P1 · · · Pk.

Then twistor space Z obtained from Z by

115

Page 116: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

InO(k + `− 1, 1)⊕O(1, k + `− 1)→ CP1×CP1,

let Z be the hypersurface

xy = P `0 P1 · · · Pk.

Then twistor space Z obtained from Z by

• removing curve in zero section cut out by P0,

116

Page 117: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

InO(k + `− 1, 1)⊕O(1, k + `− 1)→ CP1×CP1,

let Z be the hypersurface

xy = P `0 P1 · · · Pk.

Then twistor space Z obtained from Z by

• removing curve in zero section cut out by P0,

• adding two rational curves at infinity, and

117

Page 118: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Twistor Spaces for These Metrics:

H0(CP1 × CP1,O(1, 1)) = C4 ⊃ R1,3 ⊃ H3

InO(k + `− 1, 1)⊕O(1, k + `− 1)→ CP1×CP1,

let Z be the hypersurface

xy = P `0 P1 · · · Pk.

Then twistor space Z obtained from Z by

• removing curve in zero section cut out by P0,

• adding two rational curves at infinity, and

•making small resolutions of isolated singularities.

118

Page 119: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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....................................

r

rr Z

M 4

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119

Page 120: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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.................................................................

....................................

r

rr Z

M 4

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...................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.........................................................................................................

.............................................................................

...............................................................................................................................................................................................................................................................................................................................................................................................................

Lots more ALE scalar-flat Kahler surfaces now known:

120

Page 121: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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.................................................................

....................................

r

rr Z

M 4

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...................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.........................................................................................................

.............................................................................

...............................................................................................................................................................................................................................................................................................................................................................................................................

Lots more ALE scalar-flat Kahler surfaces now known:

Joyce, Calderbank-Singer, Lock-Viaclovsky. . .

121

Page 122: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Any scalar-flat Kahler surface (M4, g, J) has a

Penrose Twistor Space (Z, J),

which is once again a complex 3-manifold.

.....................................................................................................................................................................................................................................................................................................................................................................................................................................

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r

rr Z

M 4

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...............................................................................................................................................................................................................................................................................................................................................................................................................

Lots more ALE scalar-flat Kahler surfaces now known:

Joyce, Calderbank-Singer, Lock-Viaclovsky. . .

But full classification remains an open problem.

122

Page 123: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. Complete, non-compact n-manifold(Mn, g) is asymptotically locally Euclidean (ALE)if ∃ compact set K ⊂ M such that M − K ≈∐i(Rn −Dn)/Γi, where Γi ⊂ O(n), such that

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....

gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

123

Page 124: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

124

Page 125: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

125

Page 126: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

126

Page 127: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

127

Page 128: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

128

Page 129: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

129

Page 130: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

130

Page 131: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

131

Page 132: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

132

Page 133: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

133

Page 134: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

Seems to depend on choice of coordinates!

134

Page 135: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

135

Page 136: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

Bartnik/Chrusciel (1986): With weak fall-offconditions, the mass is well-defined & coordinateindependent.

136

Page 137: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

Bartnik/Chrusciel (1986): With weak fall-offconditions, the mass is well-defined & coordinateindependent.

137

Page 138: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

gjk = δjk + O(|x|1−n2−ε)

gjk,` = O(|x|−n2−ε), s ∈ L1

138

Page 139: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

Bartnik/Chrusciel (1986): With weak fall-offconditions, the mass is well-defined & coordinateindependent.

139

Page 140: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Definition. The mass (at a given end) of anALE n-manifold is defined to be

m(M, g) := lim%→∞

Γ(n2)

4(n− 1)πn/2

∫Σ(%)

[gij,i − gii,j

]νjαE

where

• Σ(%) ≈ Sn−1/Γi is given by |~x| = %;

• ν is the outpointing Euclidean unit normal;and

• αE is the volume (n− 1)-form induced by theEuclidean metric.

Bartnik/Chrusciel (1986): With weak fall-offconditions, the mass is well-defined & coordinateindependent.

140

Page 141: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

141

Page 142: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

142

Page 143: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

143

Page 144: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

144

Page 145: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

145

Page 146: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

146

Page 147: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g = −(

1− 2m%n−2

)dt2+

(1− 2m

%n−2

)−1

d%2+%2hSn−1

147

Page 148: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

148

Page 149: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Two such regions fit together to formthe wormhole metric. Scalar-flat,AE, two ends. Not Ricci-flat, butconformally flat. Same mass m atboth ends: “size of throat.”

149

Page 150: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Two such regions fit together to formthe wormhole metric. Scalar-flat,AE, two ends. Not Ricci-flat, butconformally flat. Same mass m atboth ends: “size of throat.”

150

Page 151: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Two such regions fit together to formthe wormhole metric. Scalar-flat,AE, two ends. Not Ricci-flat, butconformally flat. Same mass m atboth ends: “size of throat.”

151

Page 152: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Two such regions fit together to formthe wormhole metric. Scalar-flat,AE, two ends. Not Ricci-flat, butconformally flat. Same mass m atboth ends: “size of throat.”

152

Page 153: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Two such regions fit together to formthe wormhole metric. Scalar-flat,AE, two ends. Not Ricci-flat, butconformally flat. Same mass m atboth ends: “size of throat.”

153

Page 154: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

154

Page 155: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

But any Ricci-flat ALE manifold has mass zero.

155

Page 156: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

But any Ricci-flat ALE manifold has mass zero.

Bartnik: Ricci-flat =⇒ faster fall-off of metric!

156

Page 157: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

But any Ricci-flat ALE manifold has mass zero.

Bartnik: Ricci-flat =⇒ faster fall-off of metric!

=⇒ “gravitational instantons” have mass zero.

157

Page 158: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2⊂ C2 × CP1

158

Page 159: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0hypersurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2 ⊂ C2×CP1

159

Page 160: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

160

Page 161: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0 hy-persurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2 ⊂ C2×CP1

161

Page 162: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0 hy-persurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2 ⊂ C2×CP1

162

Page 163: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0 hy-persurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2 ⊂ C2×CP1:

ω =i

2∂∂ [u + 3m log u] , u = |z1|2 + |z2|2

163

Page 164: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0 hy-persurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2 ⊂ C2×CP1:

ω =i

2∂∂ [u + 3m log u] , u = |z1|2 + |z2|2

164

Page 165: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Motivation:

When n = 3, ADM mass in general relativity.

Reads off “apparent mass” from strength of thegravitational field far from an isolated source.

In any dimension, reproduces “mass” of t = 0 hy-persurface in (n + 1)-dimensional Schwarzschild

g =

(1− 2m

%n−2

)−1

d%2+%2hSn−1

Scalar-flat-Kahler Burns metric on C2 ⊂ C2×CP1:

ω =i

2∂∂ [u + 3m log u] , u = |z1|2 + |z2|2

also has mass m .

165

Page 166: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

166

Page 167: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

167

Page 168: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

168

Page 169: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

169

Page 170: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Physical intuition:

170

Page 171: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Physical intuition:

Local matter density ≥ 0 =⇒ total mass ≥ 0.

171

Page 172: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Physical intuition:

Local matter density ≥ 0 =⇒ total mass ≥ 0.

172

Page 173: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

173

Page 174: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

174

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

175

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

176

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n.)

177

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

178

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

Hawking-Pope 1978:

179

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

Hawking-Pope 1978:

Conjectured true in ALE case, too.

180

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

Hawking-Pope 1978:

Conjectured true in ALE case, too.

L 1987:

181

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

Hawking-Pope 1978:

Conjectured true in ALE case, too.

L 1987:

ALE counter-examples.

182

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

Hawking-Pope 1978:

Conjectured true in ALE case, too.

L 1987:

ALE counter-examples.

Scalar-flat Kahler metrics

183

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Positive Mass Conjecture:

Any AE manifold with s ≥ 0 has m ≥ 0.

Schoen-Yau 1979:

Proved in dimension n ≤ 7.

Witten 1981:

Proved for spin manifolds (implicitly, for any n).

Hawking-Pope 1978:

Conjectured true in ALE case, too.

L 1987:

ALE counter-examples.

Scalar-flat Kahler metrics

on line bundles L→ CP1 of Chern-class ≤ −3.

184

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Mass of ALE Kahler manifolds?

185

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

186

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

187

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

188

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

189

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

190

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

n = 2m ≥ 4

191

Page 192: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

192

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

Main Point:

193

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

Main Point:

Mass of an ALE Kahler manifold is unambiguous.

194

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Mass of ALE Kahler manifolds?

Scalar-flat Kahler case?

Lemma. Any ALE Kahler manifold has onlyone end.

Main Point:

Mass of an ALE Kahler manifold is unambiguous.

Does not depend on the choice of an end!

195

Page 196: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

196

Page 197: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

197

Page 198: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

198

Page 199: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

199

Page 200: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

200

Page 201: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

201

Page 202: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

That is, m(M, g, J) is completely determined by

202

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We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

That is, m(M, g, J) is completely determined by

203

Page 204: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

That is, m(M, g, J) is completely determined by

• the smooth manifold M ,

204

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We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

That is, m(M, g, J) is completely determined by

• the smooth manifold M ,

• the first Chern class c1 = c1(M,J) ∈ H2(M)of the complex structure, and

205

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We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

That is, m(M, g, J) is completely determined by

• the smooth manifold M ,

• the first Chern class c1 = c1(M,J) ∈ H2(M)of the complex structure, and

• the Kahler class [ω] ∈ H2(M) of the metric.

206

Page 207: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We begin with the scalar-flat Kahler case.

Theorem A. The mass of an ALE scalar-flatKahler manifold is a topological invariant.

That is, m(M, g, J) is completely determined by

• the smooth manifold M ,

• the first Chern class c1 = c1(M,J) ∈ H2(M)of the complex structure, and

• the Kahler class [ω] ∈ H2(M) of the metric.

In fact, we will see that there is an explicit formulafor the mass in terms of these data!

207

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The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

208

Page 209: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

209

Page 210: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

210

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The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M, g) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

211

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The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M, g) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

212

Page 213: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M,J) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

213

Page 214: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M,J) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

214

Page 215: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M,J) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

215

Page 216: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M,J) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

Note that minimality is essential here.

216

Page 217: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

The explicit formula reproduces the mass in caseswhere it previously had been laboriously computedfrom the definition. But it also allows one to quicklyread it off quite generally.

Corollary, suggested by Cristiano Spotti:

Theorem B. Let (M4, g, J) be an ALE scalar-flat Kahler surface, and suppose that (M,J) isthe minimal resolution of a surface singularity.Then m(M, g) ≤ 0, with = iff g is Ricci-flat.

Note that minimality is essential here.

Non-minimal resolutions typically admit families ofsuch metrics for which the mass can be continuouslydeformed from negative to positive.

217

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Explicit formula depends on a topological fact:

218

Page 219: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. x Then the natural map

219

Page 220: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. x Then the natural map

220

Page 221: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

221

Page 222: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

222

Page 223: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

223

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Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

224

Page 225: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Here

Hpc (M) :=

ker d : Epc (M)→ Ep+1c (M)

dEp−1c (M)

225

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Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Here

Hpc (M) :=

ker d : Epc (M)→ Ep+1c (M)

dEp−1c (M)

where

Epc (M) := Smooth, compactly supported p-forms on M.

226

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Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

227

Page 228: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

228

Page 229: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

229

Page 230: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

230

Page 231: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

♣ : H2dR(M)→ H2

c (M)

231

Page 232: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

♣ : H2dR(M)→ H2

c (M)

to denote the inverse of the natural map

232

Page 233: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

♣ : H2dR(M)→ H2

c (M)

to denote the inverse of the natural map

H2c (M)→ H2

dR(M)

induced by the inclusion of compactly supportedsmooth forms into all forms.

233

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Explicit formula depends on a topological fact:

Lemma. Let (M, g) be any ALE manifold of realdimension n ≥ 4. Then the natural map

H2c (M)→ H2

dR(M)

is an isomorphism.

Definition. If (M, g, J) is any ALE Kahler man-ifold, we will use

♣ : H2dR(M)→ H2

c (M)

to denote the inverse of the natural map

H2c (M)→ H2

dR(M)

induced by the inclusion of compactly supportedsmooth forms into all forms.

234

Page 235: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

235

Page 236: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)ofcomplex dimension m has mass given by

236

Page 237: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

237

Page 238: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

238

Page 239: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

239

Page 240: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

240

Page 241: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

241

Page 242: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

242

Page 243: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

243

Page 244: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

where

244

Page 245: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

where

• s = scalar curvature;

245

Page 246: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

where

• s = scalar curvature;

• dµ = metric volume form;

246

Page 247: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

where

• s = scalar curvature;

• dµ = metric volume form;

• c1 = c1(M,J) ∈ H2(M) is first Chern class;

247

Page 248: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

where

• s = scalar curvature;

• dµ = metric volume form;

• c1 = c1(M,J) ∈ H2(M) is first Chern class;

• [ω] ∈ H2(M) is Kahler class of (g, J); and

248

Page 249: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

where

• s = scalar curvature;

• dµ = metric volume form;

• c1 = c1(M,J) ∈ H2(M) is first Chern class;

• [ω] ∈ H2(M) is Kahler class of (g, J); and

• 〈 , 〉 is pairing between H2c (M) and H2m−2(M).

249

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m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

250

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4πm(2m−1)(m−1)!

m(M, g) = − 4π(m−1)!

〈♣(c1), [ω]m−1〉+∫Msgdµg

251

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For a compact Kahler manifold (M2m, g, J),

∫Msgdµg =

(m− 1)!〈c1, [ω]m−1〉

252

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For a compact Kahler manifold (M2m, g, J),

0 = − 4π

(m− 1)!〈c1, [ω]m−1〉 +

∫Msgdµg

253

Page 254: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

For an ALE Kahler manifold (M2m, g, J),

4πm(2m−1)(m−1)!

m(M, g) = − 4π(m−1)!

〈♣(c1), [ω]m−1〉+∫Msgdµg

254

Page 255: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

For an ALE Kahler manifold (M2m, g, J),

4πm(2m−1)(m−1)!

m(M, g) = − 4π(m−1)!

〈♣(c1), [ω]m−1〉+∫Msgdµg

So the mass is a “boundary correction” to the topo-logical formula for the total scalar curvature.

255

Page 256: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Theorem C. Any ALE Kahler manifold (M, g, J)of complex dimension m has mass given by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

256

Page 257: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We can now state our mass formula:

Corollary. Any ALE scalar-flat Kahler mani-fold (M, g, J) of complex dimension m has massgiven by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

.

257

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We can now state our mass formula:

Corollary. Any ALE scalar-flat Kahler mani-fold (M, g, J) of complex dimension m has massgiven by

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

.

So Theorem A is an immediate consequence!

258

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Rough Idea of Proof:

259

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Rough Idea of Proof:

Special Case: Suppose

260

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Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

261

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Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

262

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Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

• Complex structure J standard at infinity:

263

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Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

• Complex structure J standard at infinity:

(M −K, J) ≈bih (C2 −B4)/Γ.

264

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Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

• Complex structure J standard at infinity:

(M −K, J) ≈bih (C2 −B4)/Γ.

Since g is Kahler, the complex coordinates

265

Page 266: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

• Complex structure J standard at infinity:

(M −K, J) ≈bih (C2 −B4)/Γ.

Since g is Kahler, the complex coordinates

(z1, z2) = (x1 + ix2, x3 + ix4)

are harmonic. So xj are harmonic, too, and

266

Page 267: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

• Complex structure J standard at infinity:

(M −K, J) ≈bih (C2 −B4)/Γ.

Since g is Kahler, the complex coordinates

(z1, z2) = (x1 + ix2, x3 + ix4)

are harmonic. So xj are harmonic, too, and

267

Page 268: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Rough Idea of Proof:

Special Case: Suppose

•m = 2, n = 4;

• Scalar flat: s ≡ 0; and

• Complex structure J standard at infinity:

(M −K, J) ≈bih (C2 −B4)/Γ.

Since g is Kahler, the complex coordinates

(z1, z2) = (x1 + ix2, x3 + ix4)

are harmonic. So xj are harmonic, too, and

gjk(gj`,k − gjk,`

)ν`αE = −?d log

(√det g

)+O(%−3−ε).

268

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

269

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

Now set θ = i2(∂ − ∂)

(log√

det g), so that

270

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

Now set θ = i2(∂ − ∂)

(log√

det g), so that

ρ = dθ

is Ricci form, and

271

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

Now set θ = i2(∂ − ∂)

(log√

det g), so that

ρ = dθ

is Ricci form, and

−?d log(√

det g)

= 2 θ ∧ ω.

272

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

Now set θ = i2(∂ − ∂)

(log√

det g), so that

ρ = dθ

is Ricci form, and

−?d log(√

det g)

= 2 θ ∧ ω.Thus

m(M, g) = − lim%→∞

1

6π2

∫S%/Γ

θ ∧ ω

273

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

Now set θ = i2(∂ − ∂)

(log√

det g), so that

ρ = dθ

is Ricci form, and

−?d log(√

det g)

= 2 θ ∧ ω.Thus

m(M, g) = − lim%→∞

1

6π2

∫S%/Γ

θ ∧ ω

However, since s = 0,

d(θ ∧ ω) = ρ ∧ ω =s

4ω2 = 0.

274

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m(M, g) = − lim%→∞

1

12π2

∫S%/Γ

? d(

log√

det g)

Now set θ = i2(∂ − ∂)

(log√

det g), so that

ρ = dθ

is Ricci form, and

−?d log(√

det g)

= 2 θ ∧ ω.Thus

m(M, g) = − 1

6π2

∫S%/Γ

θ ∧ ω

275

Page 276: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:

276

Page 277: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.......

.......

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radius

1

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...........................................................................................................................................................................................................................................................................

............................................................................................

...........................................................................................

277

Page 278: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.......

.......

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radius

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...........................................................................................

278

Page 279: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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radius

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...........................................................................................

279

Page 280: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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radius

“end”

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280

Page 281: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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“end”

1

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281

Page 282: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.......

.......

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.......

.......

......................

radius

1

.............................................................................................................................................................................................................................................................

...........................................................................................................................................................................................................................................................................

............................................................................................

...........................................................................................

282

Page 283: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.......

.......

.......

.......

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......................

radius

M%

%

1

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...........................................................................................

283

Page 284: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

.......

.......

.......

.......

.......

.......

.......

.......

.......

.......

.......

.......

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.......

.......

.......

.......

.......

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.......

.......

.......

.......

.......

.......

.......

......................

radius

M%

%

1

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...............................

284

Page 285: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

285

Page 286: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

286

Page 287: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

Compactly supported, because dθ = ρ near infinity.

287

Page 288: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

288

Page 289: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 =

∫Mψ ∧ ω

289

Page 290: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 =

∫M%

ψ ∧ ω

where M% defined by radius ≤ %.

290

Page 291: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 =

∫M%

ψ ∧ ω

291

Page 292: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), ω〉 =

∫M%

[ρ− d(fθ)] ∧ ω

292

Page 293: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), ω〉 =

∫M%

[ρ− d(fθ)] ∧ ω

because scalar-flat =⇒ ρ ∧ ω = 0.

293

Page 294: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫M%

d(fθ) ∧ ω

because scalar-flat =⇒ ρ ∧ ω = 0.

294

Page 295: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫M%

d(fθ ∧ ω)

because scalar-flat =⇒ ρ ∧ ω = 0.

295

Page 296: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫M%

d(fθ ∧ ω)

296

Page 297: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫∂M%

fθ ∧ ω

by Stokes’ theorem.

297

Page 298: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫∂M%

θ ∧ ω

by Stokes’ theorem.

298

Page 299: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫S%/Γ

θ ∧ ω

by Stokes’ theorem.

299

Page 300: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫S%/Γ

θ ∧ ω

by Stokes’ theorem.

300

Page 301: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫S%/Γ

θ ∧ ω

by Stokes’ theorem.

So

m(M, g) = − 1

6π2

∫S%/Γ

θ ∧ ω

301

Page 302: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫S%/Γ

θ ∧ ω

by Stokes’ theorem.

So

m(M, g) = − 1

3π〈♣(c1), [ω]〉

302

Page 303: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Let f : M → R be smooth cut-off function:≡ 0 away from end,≡ 1 near infinity.

Set

ψ := ρ− d(fθ)

[ψ] = ♣([ρ]) = 2π♣(c1) ∈ H2c (M)

〈2π♣(c1), [ω]〉 = −∫S%/Γ

θ ∧ ω

by Stokes’ theorem.

So

m(M, g) = − 1

3π〈♣(c1), [ω]〉

as claimed.

303

Page 304: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We assumed:

304

Page 305: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

We assumed:

•m = 2;

• s ≡ 0; and

• Complex structure J standard at infinity.

305

Page 306: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

306

Page 307: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

307

Page 308: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

308

Page 309: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

309

Page 310: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

310

Page 311: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

• If m = 2 and AE, J is still standard at infinity.

311

Page 312: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

• If m = 2 and AE, J is still standard at infinity.

• If m = 2 and ALE, J can be non-standard at∞.

312

Page 313: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

• If m = 2 and AE, J is still standard at infinity.

• If m = 2 and ALE, J can be non-standard at∞.

The last point is serious.

313

Page 314: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

• If m = 2 and AE, J is still standard at infinity.

• If m = 2 and ALE, J can be non-standard at∞.

Seen in “gravitational instantons”

and other explicit examples.

314

Page 315: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

• If m = 2 and AE, J is still standard at infinity.

• If m = 2 and ALE, J can be non-standard at∞.

One argument proceeds by osculation:

315

Page 316: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

General case:

•General m ≥ 2: straightforward. . .

• s 6≡ 0, compensate by adding∫s dµ. . .

• If m > 2, J is always standard at infinity.

• If m = 2 and AE, J is still standard at infinity.

• If m = 2 and ALE, J can be non-standard at∞.

One argument proceeds by osculation:

J = J0 + O(%−3), OJ = O(%−4)

in suitable asymptotic coordinates adapted to g.

316

Page 317: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

317

Page 318: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

Let M∞ be universal over of end M∞.

318

Page 319: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

Let M∞ be universal over of end M∞.

Cap off M∞ by adding CPm−1 at infinity.

319

Page 320: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

Let M∞ be universal over of end M∞.

Cap off M∞ by adding CPm−1 at infinity.

Added hypersurface CPm−1 has normal bundleO(1).

320

Page 321: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

Let M∞ be universal over of end M∞.

Cap off M∞ by adding CPm−1 at infinity.

Added hypersurface CPm−1 has normal bundleO(1).

Complete analytic family encodes info about J .

321

Page 322: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

322

Page 323: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

AE case:

Compactify M itself by adding CPm−1 at infinity.

323

Page 324: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

AE case:

Compactify M itself by adding CPm−1 at infinity.

Linear system of CPm−1 gives holomorphic map

(M ∪ CPm−1)→ CPmwhich is biholomorphism near CPm−1.

324

Page 325: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

AE case:

Compactify M itself by adding CPm−1 at infinity.

Linear system of CPm−1 gives holomorphic map

(M ∪ CPm−1)→ CPmwhich is biholomorphism near CPm−1.

Thus obtain holomorphic map

Φ : M → Cm

which is biholomorphism near infinity.

325

Page 326: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

To understand J at infinity:

AE case:

Compactify M itself by adding CPm−1 at infinity.

Linear system of CPm−1 gives holomorphic map

(M ∪ CPm−1)→ CPmwhich is biholomorphism near CPm−1.

Thus obtain holomorphic map

Φ : M → Cm

which is biholomorphism near infinity.

This has some interesting consequences. . .

326

Page 327: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

327

Page 328: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

328

Page 329: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

329

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Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

330

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Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

AE & Kahler & s ≥ 0 =⇒ m(M, g) ≥ 0.

331

Page 332: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

AE & Kahler & s ≥ 0 =⇒ m(M, g) ≥ 0.

Moreover, m = 0 ⇐⇒

332

Page 333: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

AE & Kahler & s ≥ 0 =⇒ m(M, g) ≥ 0.

Moreover, m = 0⇐⇒ (M, g) is Euclidean space.

333

Page 334: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem D (Positive Mass Theorem). Any AEKahler manifold with non-negative scalar curva-ture has non-negative mass:

AE & Kahler & s ≥ 0 =⇒ m(M, g) ≥ 0.

Moreover, m = 0⇐⇒ (M, g) is Euclidean space.

Proof actually shows something stronger!

334

Page 335: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

335

Page 336: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

336

Page 337: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

337

Page 338: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

338

Page 339: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

339

Page 340: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

340

Page 341: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

341

Page 342: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

342

Page 343: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

343

Page 344: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

m(M, g) ≥ (m− 1)!

(2m− 1)πm−1

∑njVol (Dj)

344

Page 345: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

m(M, g) ≥ (m− 1)!

(2m− 1)πm−1

∑njVol (Dj)

345

Page 346: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

m(M, g) ≥ (m− 1)!

(2m− 1)πm−1

∑njVol (Dj)

346

Page 347: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

m(M, g) ≥ (m− 1)!

(2m− 1)πm−1

∑njVol (Dj)

with = ⇐⇒

347

Page 348: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Theorem E (Penrose Inequality). Let (M2m, g, J)be an AE Kahler manifold with scalar curvatures ≥ 0. Then (M,J) carries a canonical divisorD that is expressed as a sum

∑jnjDj of com-

pact complex hypersurfaces with positive integercoefficients, with the property that

⋃jDj 6= ∅

whenever (M,J) 6= Cm. In terms of this divi-sor, we then have

m(M, g) ≥ (m− 1)!

(2m− 1)πm−1

∑njVol (Dj)

with = ⇐⇒ (M, g, J) is scalar-flat Kahler.

348

Page 349: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

349

Page 350: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

350

Page 351: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

of the canonical line bundle which vanishes exactlyat the critical points of Φ.

351

Page 352: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

of the canonical line bundle which vanishes exactlyat the critical points of Φ.

352

Page 353: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

of the canonical line bundle which vanishes exactlyat the critical points of Φ.

The zero set of ϕ, counted with multiplicities, givesus a canonical divisor

353

Page 354: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

of the canonical line bundle which vanishes exactlyat the critical points of Φ.

The zero set of ϕ, counted with multiplicities, givesus a canonical divisor

D =∑

njDj

354

Page 355: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

of the canonical line bundle which vanishes exactlyat the critical points of Φ.

The zero set of ϕ, counted with multiplicities, givesus a canonical divisor

D =∑

njDj

and

−〈♣(c1),ωm−1

(m− 1)!〉 =

∑njVol (Dj)

355

Page 356: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

This follows from existence of a holomorphic map

Φ : M → Cm

which is a biholomorphism near infinity.

Indeed, we then have a holomorphic section

ϕ = Φ∗dz1 ∧ · · · ∧ dzm

of the canonical line bundle which vanishes exactlyat the critical points of Φ.

The zero set of ϕ, counted with multiplicities, givesus a canonical divisor

D =∑

njDj

and

−〈♣(c1),ωm−1

(m− 1)!〉 =

∑njVol (Dj)

so the mass formula implies the claim.

356

Page 357: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

357

Page 358: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

358

Page 359: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

359

Page 360: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

360

Page 361: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

m(M, g) = −〈♣(c1), [ω]m−1〉(2m− 1)πm−1

+(m− 1)!

4(2m− 1)πm

∫Msgdµg

...............................................................................................................................................................................................................................................................................................................................

...............................................................................................................................................................................................................................................................................................................................

.....................................................................................................................................................................................................................................................................................................................................................................................................

................................................................................. .....................................................

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..................................

..................................

..................................................

.....................

...............................

361

Page 362: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

362

Page 363: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Happy Birthday, Roger!

363

Page 364: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Happy Birthday, Roger!

Happy Birthday, Twistors!

364

Page 365: Stony Brook University New Horizons in Twistor Theory ...people.maths.ox.ac.uk/lmason/New Horizons/Claude-Lebrun.pdf · K ahler Geometry Claude LeBrun Stony Brook University New Horizons

Happy Birthday, Roger!

Happy Birthday, Twistors!

Happy Non-Retirement, Nick!

365


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