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Constraining Dark Matter Annihilation to Gamma Rays and Charged Particles Thomas Jacques 2009-07, Seattle Based on work with N. Bell, J. Beacom, G. Mack, H. Yuksel
Constraining Dark Matter Annihilation to Gamma Rays
and Charged ParticlesThomas Jacques
2009-07, Seattle
Based on work withN. Bell, J. Beacom, G. Mack, H. Yuksel
IntroductionExistence √
Rotation Curves, Gravitational Lensing, Bullet Cluster, Cosmic Microwave Background, Big Bang Nucleosynthesis, Large Scale Structure, etc.
Thomas Jacques - INT 09-2A 2009.06
Indirect DetectionProperties?
Plenty of candidates - Which is DM?
Indirect detection often focuses on choosing a model, and comparing predicted flux to observed flux
Great for testing a model, not so great for finding the nature of DM
Thomas Jacques - INT 09-2A 2009.06
Indirect DetectionProperties?
Plenty of candidates - Which is DM?
Indirect detection often focuses on choosing a model, and comparing predicted flux to observed flux
Great for testing a model, not so great for finding the nature of DM
Thomas Jacques - INT 09-2A 2009.06
So, what can we deduce about DM, in a model independent way, from it’s annihilation flux?
Great progress in recent years; A number of bounds on annihilation cross section/decay width
We expand and strengthen these limits, focusing on two final states, γγ and e+e-, and determining conservative upper limits on the annihilation cross section 〈σAv〉, so we can be confident that these are robust upper limits
Previous Bounds
Thomas Jacques - INT 09-2A 2009.06
!
!
"
"
γγPhoton line
‘Smoking Gun’
Fairly Universal, even if small branching
Don’t know branching ratio: Gives an upper limit for this channel only
from Mack, Jacques, Beacom, Bell, Yuksel; Phys.Rev.D78:063542 (2008)Thomas Jacques - INT 09-2A 2009.06
γ
γχ
χ
d!!
dE=
12!!Av"Br("")
! R
0
#(s)2
4$m2"
d%dN!
dE
Annihilation FluxAnnihilation flux from a nearby source:
Thomas Jacques - INT 09-2A 2009.06
d!!
dE=
12!!Av"Br("")
! R
0
#(s)2
4$m2"
d%dN!
dE
Annihilation FluxAnnihilation flux from a nearby source:
Flux in some direction depends on:
Thomas Jacques - INT 09-2A 2009.06
d!!
dE=
12!!Av"Br("")
! R
0
#(s)2
4$m2"
d%dN!
dE
Annihilation FluxAnnihilation flux from a nearby source:
Flux in some direction depends on: Cross section,
Thomas Jacques - INT 09-2A 2009.06
d!!
dE=
12!!Av"Br("")
! R
0
#(s)2
4$m2"
d%dN!
dE
Annihilation FluxAnnihilation flux from a nearby source:
Flux in some direction depends on: Cross section,Integral along the line of sight of the DM density squared,
Thomas Jacques - INT 09-2A 2009.06
d!!
dE=
12!!Av"Br("")
! R
0
#(s)2
4$m2"
d%dN!
dE
Annihilation FluxAnnihilation flux from a nearby source:
Flux in some direction depends on: Cross section,Integral along the line of sight of the DM density squared,The γ-ray spectrum per annihilation (Dirac delta)
Thomas Jacques - INT 09-2A 2009.06
Annihilation FluxAnnihilation flux from a nearby source:
Thomas Jacques - INT 09-2A 2009.06
d!!
dE=
!!Av"2
J!"
J0
14"m2
"
dN!
dEγγ
Density profilesMinimize uncertainty by looking at large angular regions
Focus on conservativeKravtsov profile, but show results for other profiles
NFW and Einastoprofiles most widelyused in literature
301
Thomas Jacques - INT 09-2A 2009.06
Observation RegionsGalactic Center
Our main flux source; lots of data
M31 (Andromeda)
Relatively weak upper limits on 〈σAv〉Analysis very similar to GC case
Cosmic Annihilation
Diffuse photon flux from extragalactic DM annihilation
Analysis includes integral over redshift, photon attenuation, DM clumping factor
Thomas Jacques - INT 09-2A 2009.06
Data
Use data from INTEGRAL, COMPTEL, EGRET, HEGRA, CELESTE, HESS, SMM
Cover broad range of energies: ~10-5 to ~104 GeV
Thomas Jacques - INT 09-2A 2009.06
Results
10-5
10-3
10-1
101
103
105
m! [GeV]
10-34
10-32
10-30
10-28
10-26
10-24
10-22
10-20
< "
Av
>##
[c
m3
s-1]
DIFFUSE PHOTON BACKGROUND
INTE
GRAL
CGRO MW
EGRET
M31
CELESTE
M31
HEGRA M31
HESS GC RIDGE
Thomas Jacques - INT 09-2A 2009.06
Very conservative analysis
Results more general than they appear: We integrate the signal over a large energy bin, so results are valid for an annihilation spectrum as wide as our analysis bin (0.4 in log10 E)
At worst, our limit would be increased by a factor of several for a broad annihilation spectrum (except for INTEGRAL/HEGRA)
Using Br(γγ) = 10-4, find a limit on the total cross section
10-5
10-3
10-1
101
103
105
m! [GeV]
10-30
10-28
10-26
10-24
10-22
10-20
10-18
10-16
< "
Av
>to
tal
[cm
3 s-1
]
Natural Scale
Br(##!=10-4
Unitarity B
ound
Neutrinos
KKT
Gamma RaysBr($$!=1
Thomas Jacques - INT 09-2A 2009.06
Results
Positron Excess
Fermi e+e- excessPhys. Rev. Lett. 102, 181101 (2009)
PAMELA Positron excessNature 458, 607-609
Thomas Jacques - INT 09-2A 2009.06
Positron Excess
from N. Bell & T. Jacques; Phys.Rev.D79:043507 (2008)Thomas Jacques - INT 09-2A 2009.06
Positron Excess
from N. Bell & T. Jacques; Phys.Rev.D79:043507 (2008)
Nearby Pulsars?
Dark Matter Annihilation?
No antiproton excess
Large annihilation cross section
Thomas Jacques - INT 09-2A 2009.06
Positron ExcessWant to constrain annihilation to e+e-
Look for associated gamma-ray emission
from N. Bell & T. Jacques; Phys.Rev.D79:043507 (2008)
Nearby Pulsars?
Dark Matter Annihilation?
No antiproton excess
Large annihilation cross section
Thomas Jacques - INT 09-2A 2009.06
Positron ExcessWant to constrain annihilation to e+e-
Look for associated gamma-ray emission
from N. Bell & T. Jacques; Phys.Rev.D79:043507 (2008)
Nearby Pulsars?
Dark Matter Annihilation?
No antiproton excess
Large annihilation cross section
Thomas Jacques - INT 09-2A 2009.06
!
!
e+
e!Internal Bremsstrahlung
No dependence on Magnetic field, ISRF, Diffusion
Hard gamma rays near the endpoint, and background decreases with energy
Internal Brem SpectrumSimilar to analysis for gamma-gamma case
Different spectrum
d!IB
dE= !tot !
"
E#
!ln
"s!
m2e
#" 1
$!1 +
"s!
s
#2$
dN!
dE=
1!tot
d!IB
dE!
s=4mχ2 s’=4mχ(mχ-E)
d!!
dE=
!!Av"2
J!"
J0
14"m2
"
dN!
dE
Beacom, Bell, Bertone, Phys.Rev.Lett.94:171301 (2005)Thomas Jacques - INT 09-2A 2009.06
100 1000E [GeV]
1
10
100
E2 dNγ /
dE [G
eV a
nnih
ilatio
n-1]
Constraints
Thomas Jacques - INT 09-2A 2009.06
10-3 10-2 10-1 100 101 102 103 104 105
mχ [GeV]
10-32
10-30
10-28
10-26
10-24
10-22
10-20
10-18
10-16
Br(ii
) < σ
Av
> tota
l [cm
3 s-1
]
Natural Scale
γγ
νν
e+e-
KKT
Unitarity Bound
µ+µ
-
τ+τ
-
10-3 10-2 10-1 100 101 102 103 104 105
mχ [GeV]
10-2810-2710-2610-2510-2410-2310-2210-2110-20
<σA
v>e+ e- [
cm3 s-1
]
COMPTEL
EGRET
CELES
TEH.E.S.S.
Natural Scale
S-wave annihilation of Majorana particles to fermion pairs is often suppressed by a factor of mf2
IB emission of hard gamma rays from the propagator can lift this suppression, making Br(f f γ) significantly larger than Br(f f)
This would improve our limits by a significant factor
Helicity Suppression
eg Bergstrom, Phys.Lett.B 225, 372 (1989)Bringmann, Bergstrom, Edsjo, JHEP 0801, 049 (2008)
!
!
e+
"
e!
!
!
e+
"
e!
Thomas Jacques - INT 09-2A 2009.06
Cirelli, Kadastik, Raidal & Strumia arXiv:0809.2409
Comparison
Thomas Jacques - INT 09-2A 2009.06
Summary
We have placed model independent constraints on the Dark Matter annihilation cross section to various final states
Examined γγ, e+e-, µ+µ-, τ+τ-
γγ constraints valid for moderately broad annihilation spectra
Extremely conservative analysis
Thomas Jacques - INT 09-2A 2009.06
