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Neutrino Mass Physics at LHC
R. N. MohapatraUniversity of MarylandNO-VE, 2008, Venice
Two broad new kinds of physics for neutrino mass:
(i) Why ? (new scale, new particles, ..)
(ii) Why two mixing angles are so large ?
(new flavor symmetries or GUTs ?)
lqmm ,
Small neutrino mass and Seesaw mechanism
Why ? Seesaw solution: Add right handed
neutrinos to SM with Majorana mass:
new
Breaks B-L : New scale, new symmetry and new physics beyond SM.
After electroweak symmetry breaking
leads to seesaw formula:
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Seesaw Mechanism After Electroweak Sym Breaking mass matrix is given by
which gives (type I seesaw)
Minkowski,Gell-Mann, Ramond, Slansky,Yanagida,R.N.M.,Senjanovic,Glashow
),( N
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Seesaw and B-L symmetry SM Higgs boson represents physics of the
electroweak symmetry breaking and its discovery will complete understanding of SM symmetry.
Seesaw mechanism tells us that there is a new symmetry breaking scale associated
with RH neutrino mass: B-L symmetry . This talk discusses how to search for the
Higgs fields associated with this symmetry and improve our understanding of B-L symmetry.
Testing the seesaw idea and B-L symmetry.
Important for testing seesaw are two considerations:
(i) How big is the seesaw or B-L scale ?
(ii) What is the new physics associated with this new scale ? –are there new forces, new Higgs fields, etc ?
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Seesaw with no new forces at LHC
If there is no new interaction: Only way to test seesaw is to produce N; This can happen only through mixing if is in sub-TeV range and further only if mixing is > (del Aguila,Aguilar-Savedra,
Pittau; Han, Zhang…) – However Tiny and 100 GeV implies and ; can only be
large under highly contrived cases:(Kersten, Smirnov) ; Unlikely to test seesaw this way!
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5.510h
N 610
N NM
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Situation changes drastically with new interactions: With new gauge forces coupled to RH
neutrinos, seesaw can be tested despite tiny ;
A simple possibility is where there is a
B-L gauge force coupling to matter as part of an
gauge symmetry. RH neutrino mass in this case is associated with the
breaking of this new symmetry . This provides new signals for seesaw
at LHC.
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LBRL USUSU )1()2()2(
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Two well motivated scenarios:
(i) Large Grand unification is an independently well motivated
hypothesis which suggests for Yukawa coupings:
implying GeV
Gauge coupling unification scale High scale seesaw goes well with GUT s; e.g. SO(10).
However in this case, few signals of seesaw: One direct test is search for assuming susy ! GUTs have problems too: doublet triplet splitting; vs
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Lower scale non-GUT type seesaw: Subject of this talk: (ii) Small Yukawas: Note the dependence of in the seesaw formula compared to linear on for ; so not too small
Yukawas can lead to e.g. Implies seesaw or B-L physics scale in few TeV range. In general scale far below GUT scale- Simple example is - low scale left-right model.
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SUSY LR attractive for other reasons: Supersymmetric left-right model: (i) Expialns the origin of parity violation: (ii) Solves gauge hierarchy problem (as in
MSSM); (iii) Gives automatic R-parity (unlike
MSSM) and hence natural neutralino dark matter and naturally stable proton.
(iv) Solves susy CP and strong CP problem (unlike MSSM).
(v) Helps in understanding a supersymmetry breaking mechanism (unlike MSSM).
SUSYLR DETAILS:
Gauge group: Fermion assignment
Higgs fields
(R.N.M., Senjanovic, 79)
LBRL USUSU )1()2()2(
L
L
d
u
R
R
d
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)0,2,2( )2,1,3()2,3,1(; LR
Detailed Higgs content and Sym Breaking
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Break symmetry and give fermion masses
.. RRRLRqY LLLQQQhL f
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SUSY essential for lower scale left-right seesaw
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Without SUSY neutrino mass too large since v_L~GeV. (type I+II seesaw) , SUSY implies ; (pure type I seesaw) nu-mass in the eV range even for TeV seesaw.
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SUSY breaking constraints and sub-TeV - Higgs An important question in supersymmetry
is: how is supersymmetry broken ? Scenarios: (i) Minimal Supergravity: FCNC problem (ii) Gauge mediation (needs many
particles, does not have cold dark matter etc.) (iii) Anomaly mediation: (potential to solve
both these problems.)(Randall, Sundrum; Giudice, Luty, Murayama, Rattazzi)
Consistency of case iii with electric charge conservation requires sub-TeV - Higgs
LR ,
Two cases with LHC signal (i) Multi-TeV scale WR: In this case, Sub-TeV to TeV scale WR, Z’, which can be searched for
in colliders: (ii) Higher scale B-L (or WR): New result: If , one will have in the sub-TeV range and
observable. Searching for Higgses can probe
B-L scale upto .
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LHC signals of TeV mass WR case: (A) Looking for TeV scale at LHC : Signal: Very little background; already used in
D0, CDF ; Present limits: 780 GeV (Keung, Senjanovic, 83) (Does not depend on )
LHC reach 4 TeV (Azuelos et al)
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(B): New Relaxed Upper bound on light Higgs mass
MSSM: Light Higgs mass: GeV For Low scale WR, new contribution from
D-term+ 1-loop
Zhang,RNM,Ji,An arXiv:0804.0268
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22
RW
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TeV and Higher scale Seesaw and Higgs
A generic prediction of all these models: doubly charged Higgs and Higgsinos, triplet Higgses
( , )in the TeV range – without fine tuning.
Different from triplet Higgs of type II seesaw models discussed in Perez,Han, Huang, Wang,Li, Si, Akeroyd,Aoki, Sugiyama; ……
Different from usual SUSY models which only have neutral and singly charged Higgs
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Doubly charged Higgs: Very different from known Higgs in that it couples
only to leptons and not to quarks: Coupling not small.
One coupling to left and another to the right sector:
Both decay to lepton pairs (from coupling)
For left Delta,
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R
LR
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Difference from type II models
In type II models, it is only the triplet that is present; its coupling f to leptons depends on
the < >=v since
So only for eV vev for f is measurable; Pro: it tracks neutrino mass matrices; Measuring
different branching ratios gives neutrino mass matrix
Con: such small vevs come out naturally only if triplets are superheavy and beyond the reach of LHC. One needs to do a severe fine tuning (~ )
The models I discuss are not fine tuned:
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Difference of type II models from type I: Type II: decays:
Whereas for type I models we discuss:
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Present lower bounds on doubly charged Higgs mass:
Drell-Yan pair production main mechanism at hadron colliders: Signal: pp --> or all muon
Collider: CDF, D0: GeV HERA > 141 GeV Low energy: Muonium-anti-muonium osc. (PSI)
For , M++ >250 GeV. g-2 of muon: 100 GeV order.
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Production process: Drell-Yan via exchange;
Signal: peak in like sign lepton invariant
mass plot for double charged case;
trilepton + missing E in case.
WZ ,, Zqq ,
Wdu
,
LHC prospects: Gunion, Loomis and Petit; Akyroid, Aoki; Azuelos et al.,
Mukhopadhyaya,Han,Wang,Si; Huitu,Malaampi,Raidal; Dutta..
Main Bg ZZ production: LHC Mass Reach ~TeV
with 300 fb^-1.
Doubly charged Higgs reach:
Muonium-anti-muonium can provide better probe for some models:
If SUSY is broken by anomalies: and also M < 10 TeV.
Lower limit on
PRISM expt. Reach:
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Doubly charged Higgs atCollider ee
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collider at 1 TeV cm E can probe doubly charged Higgs upto 900 GeV mass. (Mukhopadhyay, S. Rai)
The relevant processes:
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Singly charged signal Properties of singly charged
different from MSSM singly charged couples only to leptons- has L=2
Present bound on mass comes from wrong kind of muon decay:
and nuTeV expt looking for
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Bounds on NuTeV bound (Formaggio et al, 2001)
Mass bound in 100 GeV range for reasonable values of f-couplings.
New proposal NUSONG expt (Conrad et al. 2007) will improve this limit by a factor of 4 .
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AT LHC LHC signal: pp + missing E K. Wang et al.
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Why are naturally light even for high scale seesaw ?
(i) If LR scale is less than few TeV , clearly these Higgs can have in the sub-TeV mass.
(ii) For higher scale seesaw accidental global symmetry leads to sub-TeV
as long as or less. (iii) If SUSY is broken by anomaly
mediation, these fields with sub-TeV to TeV masses become essential to avoid electric charge non-conservation. Strongest case for light .
,
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Basic point is the constraint of supersymmetry:
SM Minimum corresponds to: Conserves electric charge. Higgs mass prop to and hence Higgs mass arbitrary. Bring in Supersymmetry: and
hence an upper limit on Higgs mass <130 GeV.
For SUSYLR seesaw models, SUSY constrains the Higgs potential so much that
Necessary consequence is light below 10 TeV . Otherwise, electric charge broken by vacuum.
22 )()( V
0
v 0
2v 2g
Light Higgs for High seesaw scale
Naïve logic: Higgs mass is of the order of symmetry breaking scale; breaks down when there are accidental symmetries.
SUSYLR superpotential:
Has U(6,c) global symmetry which breaks down to U(5,c) (in the absence of higher dim term.)
eleven massless complex Higgs bosons: 3 absorbed in gauge sym. breaking from SU(2)xU(1) to U(1). Eight left are two doubly charged Higgs bosons and two SM triplets;
,
,...)( ccW
How do get masses ? The nonrenormalizable term
Where could be the new physics scale above WR scale or Planck scale.
Breaks this enhanced global symmetry and give mass to fields.
Mass is of order: ;
implying for Delta mass sub-TeV. (Aulakh, Melfo, Senjanovic; Chacko, RNM, 97)
Observation of probes seesaw scale far below GUT scale.
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Anomaly mediation and light
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So for the case of MSSM+AMSB, slepton mass squares negative-vacuum breaks electric charge:
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Squark and slepton masses in AMSB:
Slepton masses in SUSYLR +AMSB
)])(([16
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Where f is the Yukawa coupling and g is the generic gauge coupling: slepton masses become positive if
SUSYLR cures the tachyonic slepton problem of AMSB without fine tuning assumptions:(Setzer, Spinner, RNM, Phys. Rev. D and arXiv:0802.1208- JHEP )
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Limit on Higgs mass, couplings from detailed study: For AMSB cure to work, we must have
(i)
(ii) ;also triplets.
This implies Prism proposal:
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Summary and Conclusion: Minimal SUSY seesaw in conjunction with
a way to understand SUSY breaking (AMSB) predicts the existence of sub-TeV
They can be observable in LHC as well as in muonium-anti-muonium oscillation
experiments. In particular it predicts:
Search for Delta Higgses can probe seesaw below
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Summary and Conclusion: (i) < few TeVs or
(ii) > GeV ;
(iii) If SUSY is broken by anomaly mediation, then
GeV (iii) In these models, there are 100 GeV to TeV scale SU(2)-triplet and doubly charged Higgs fields. (iv) Case (i)- Upward shift of light Higgs mass
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Range of Double charged Higgs masses
Upper limit for AMSB to work:
Lower limit on muonium-anti-muonium oscillation amplitude for this model (PSI)
Higher precision search for important. TeV scale WR models have many collider
tests: e.g. Higher Higgs mass, like sign dilepton
events and of course sub-TeV scale doubly charged Higgs
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Dark matter issue: Neutralino unstable ! But gravitino though unstable due to R-P
breaking but still quite long lived to be dark matter:
Decay diagram:
Longer than the age of the universe ! (Ibarra,
et al)
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Displaced vertices: Neutralino decays but with a nano to pico sec.
lifetime; hence leads to displaced vertices:
(Zhang, Nussinov, et al. to appear)
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1
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Constraints on WR in SUSYLR : Theory details
Higgs superfields break SU(2)_R
V=V_F+V_D+V_S (V_F,V_D >0)
Look for minimum of the potential
0
)2,1,3()2,1,3(
What is the smallest value of the D-term ?
When is =0
Since in general
If RP conserved i.e. V is minimum when V_D vanishes and that occurs
when: since
But this breaks electric charge !
cc
0
0
v
vc 0)( 11 mTr
0~ c
Charge conservation-> RP violation
So only choice left to get a charge conserving minimum is when
It breaks R-parity and Lepton number but not
Baryon number. So proton stability is guaranteed. Corollary: Seesaw scale has an upper limit
of a few TeV. (Kuchimanchi, RNM, 95)
0
00
Rv0~ c
Why GeV ? As the seesaw scale increases, higher dim
terms in superpotential become important : restore R-parity and give a stable charge conserving vacuum:
Typically, they are (if no new physics till Planck-otherwise replace by new Phys scale)
+
Lower limit on WR when above terms are of order weak scale i.e. >
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cc
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Tr 2)( P
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How do they get masses ?
The second nonrenormalizable term
breaks this enhanced global symmetry and give mass to fields.
Mass is of order: ; LEP bound then implies
GeV implying v_R
(Aulakh, Melfo, Senjanovic; Chacko, RNM, 97)
P
cc
M
Tr 2)(
100M
Range of Double charged Higgs masses
Upper limit for AMSB to work:
Lower limit on muonium-anti-muonium oscillation amplitude for this model (PSI)
Higher precision search for
important.
TeVM 10
MM
5106
FeeGA
LHC signals of low scale seesaw (i) TeV scale : Signal: Very little background; already
used in D0, CDF ; Present limits: 780 GeV (Keung, Senjanovic, 83)
(ii) I will focus on Higgs boson tests
',ZWR
Xjjpp
Signals for TeV scale WR’s etc.
First issue: Is there a dark matter ? Yes. It is the gravitino; it is unstable due
to R-P breaking but still quite long lived. Decay diagram:
Longer than the age of the universe !
g~
ql,
ql ~,~
lq,
cdc
m
mM
Y g
lPl
dc
g 3
5~
2
2~
~192
~
GeV4410