Indirect signatures ofGravitino Dark Matter
Alejandro Ibarra
DESY
In collaboration with
W. Buchmuller, L. Covi, K. Hamaguchi and T. Yanagida (JHEP 0703:037, 2007)
G . Bertone, W. Buchmuller, L. Covi (JCAP11(2007)003)
D. Tran (Phys.Rev.Lett.100,061301 (2008) and arXiv:0804.4596)
Planck’08Barcelona20th May 2008
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.1/33
IntroductionMany evidences of dark matter at different scales
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.2/33
IntroductionMany evidences of dark matter at different scales
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.2/33
IntroductionMany evidences of dark matter at different scales
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.2/33
IntroductionMany evidences of dark matter at different scales
The main features of any dark matter candidate are:
⋆ weakly interacting
⋆ cold (may be warm)
⋆ long lived (not necessarily stable)!
lifetime > age of the Universe (∼ 1017s)
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.2/33
Candidates for dark matterMany! Some interesting candidates are:
Massive SM neutrinos (now excluded)
Axions
Heavy sterile neutrinos
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.3/33
Candidates for dark matterMany! Some interesting candidates are:
Massive SM neutrinos (now excluded)
Axions
Heavy sterile neutrinos
Neutralinos (requires R-parity conservation)
Gravitinos
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.3/33
Candidates for dark matterMany! Some interesting candidates are:
Massive SM neutrinos (now excluded)
Axions
Heavy sterile neutrinos
Neutralinos (requires R-parity conservation)
Gravitinos
Axinos
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.3/33
Candidates for dark matterMany! Some interesting candidates are:
Massive SM neutrinos (now excluded)
Axions
Heavy sterile neutrinos
Neutralinos (requires R-parity conservation)
Gravitinos
Axinos
Lightest Kaluza-Klein particles (B1, KK graviton), scalarsinglets, Q-balls, branons, WIMPzillas, mini-black holes,cryptons, monopoles...
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.3/33
Gravitino dark matterThe gravitino is present in any theory with local supersymmetry. When thegravitino is the lightest supersymmetric particle, it constitutes a veryinteresting (and promising!) candidate for the dark matter of the Universe.
Gravitinos are thermally produced in the early Universe by QCDprocesses. For example:
+
ga
gb gc
Ggc
+
ga
gb gc
G
ga +
ga
gb gc
G
gb
ga
gb gc
G
Also produced by non-thermal processes (inflaton decay, NLSP decay)
The existence of relic gravitinos is unavoidable. Whether they constitutethe dark matter or not is just a quantitative question.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.5/33
From M. Bolz
The interactions of the gravitino with the MSSM particles are fixed bythe symmetries
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.6/33
The interactions of the gravitino with the MSSM particles are fixed bythe symmetries
The relic abundance is calculable in terms of very few parameters
Ω3/2h2≃ 0.27
(TR
1010 GeV
) (100GeV
m3/2
) ( meg
1 TeV
)2
NICELY COMPATIBLE WITH LEPTOGENESIS!
(TR >∼
109GeV)
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.6/33
The interactions of the gravitino with the MSSM particles are fixed bythe symmetries
The relic abundance is calculable in terms of very few parameters
Ω3/2h2≃ 0.27
(TR
1010 GeV
) (100GeV
m3/2
) ( meg
1 TeV
)2
NICELY COMPATIBLE WITH LEPTOGENESIS!
(TR >∼
109GeV)
However, it is undetectable in dark matter searches (direct and indirect)This is a disadvantage rather than a problem.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.6/33
The ultimate goal would be to construct a consistent thermal history ofthe Universe.
There seems to be a conflict between these three paradigms:
⋆ Supersymmetric dark matter
⋆ Big Bang Nucleosynthesis
⋆ Leptogenesis (TR >∼
109 GeV)
The extremely weak interactions of the gravitino can be veryproblematic in the early Universe
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.7/33
If R-parity is conserved, the NLSP can only decay into gravitinos andSM particles, with a decay rate suppressed by MP :
ΓNLSP ≃m5
NLSP
48πm23/2M
2P
=⇒ very long lifetimes.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.8/33
If R-parity is conserved, the NLSP can only decay into gravitinos andSM particles, with a decay rate suppressed by MP :
ΓNLSP ≃m5
NLSP
48πm23/2M
2P
=⇒ very long lifetimes.
The leptogenesis constraint TR >∼
109 GeV requires for gravitino darkmatter m3/2 >∼ 5 GeV. Then,
τNLSP ≃ 2 days( m3/2
5 GeV
)2(
150GeV
mNLSP
)5
The NLSP is present during and after BBN. The decays couldjeopardize the abundances of primordial elements.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.8/33
Summary of the implications of a high reheat temperature (TR >∼
109 GeV)for gravitino dark matter:
gravitino LSPSee talk by Kazunori Kohri
neutralino NLSP RH stau NLSP other candidates
?
HH
HH
HHj
? ? ?
χ01 → ψ3/2 hadrons Catalytic production
of 6LiHadrodissociation ofprimordial elements
stopLH sneutrinoRH sneutrino
Conflict with BBN Conflict with BBN
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.9/33
Summary of the implications of a high reheat temperature (TR >∼
109 GeV)for gravitino dark matter:
gravitino LSPSee talk by Kazunori Kohri
neutralino NLSP RH stau NLSP other candidates
?
HH
HH
HHj
? ? ?
χ01 → ψ3/2 hadrons Catalytic production
of 6LiHadrodissociation ofprimordial elements
stopLH sneutrinoRH sneutrino
Conflict with BBN Conflict with BBN
BBN is the Achilles’ heel of gravitino dark matter
Root of all the problems: the NLSP is very long lived.
Simple solution: get rid of the NLSP before BBN −→ R-parity violation
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.9/33
Gravitino DM with broken R-parity⋆ When R-parity is broken, the superpotential reads:
W = WRp + µi(HuLi) + 12λijk(LiLj)e
ck + λ′
ijk(QiLj)dck + λ
′′
ijk(ucidcjdck)
The coupling λijk induces the decay of the right-handed stau. For example,
eτR → µ ντ with lifetime:
τeτ ≃ 103s`
λ10−14
´−2 ` meτ100 GeV
´−1
Even with a tiny amount of R-parity violation (λ >∼
10−14)
the stau will decay before the time of BBN.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.10/33
Gravitino DM with broken R-parity⋆ When R-parity is broken, the superpotential reads:
W = WRp + µi(HuLi) + 12λijk(LiLj)e
ck + λ′
ijk(QiLj)dck + λ
′′
ijk(ucidcjdck)
The coupling λijk induces the decay of the right-handed stau. For example,
eτR → µ ντ with lifetime:
τeτ ≃ 103s`
λ10−14
´−2 ` meτ100 GeV
´−1
Even with a tiny amount of R-parity violation (λ >∼
10−14)
the stau will decay before the time of BBN.
⋆ The lepton/baryon number violating couplings λ, λ′, λ′′ can erase thelepton/baryon asymmetry. The requirement that an existing baryon asymmetry is
not erased before the electroweak transition implies:Campbell, Davidson, Ellis, OliveFischler, Giudice, Leigh, PabanDreiner, Ross
λ, λ′ <∼ 10−7
Plenty of room! 10−14 <∼ λ, λ′ <∼ 10−7. In this range leptogenesis is unaffected.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.10/33
⋆ Interestingly, even though the gravitino is no longer stable, it still constitutes aviable dark matter candidate. It decays for example ψ3/2 → νγ, with lifetime:
τ3/2 ∼ 1026s`
λ10−7
´−2“
m3/2
10 GeV
”−3
(Remember: age of the Universe ∼ 1017s)
Stable enough to constitute the dark matter of the Universe. Takayama, Yamaguchi
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.11/33
⋆ Interestingly, even though the gravitino is no longer stable, it still constitutes aviable dark matter candidate. It decays for example ψ3/2 → νγ, with lifetime:
τ3/2 ∼ 1026s`
λ10−7
´−2“
m3/2
10 GeV
”−3
(Remember: age of the Universe ∼ 1017s)
Stable enough to constitute the dark matter of the Universe. Takayama, Yamaguchi
In summary: A scenario with the gravitino as LSP with a mass in the range
5-300 GeV, and a small amount of R-parity violation, 10−14 <∼ λ, λ′ <∼ 10−7,
provides a good candidate for dark matter and provides a consistent thermalhistory of the Universe (allows leptogenesis and successful BBN).
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.11/33
⋆ Interestingly, even though the gravitino is no longer stable, it still constitutes aviable dark matter candidate. It decays for example ψ3/2 → νγ, with lifetime:
τ3/2 ∼ 1026s`
λ10−7
´−2“
m3/2
10 GeV
”−3
(Remember: age of the Universe ∼ 1017s)
Stable enough to constitute the dark matter of the Universe. Takayama, Yamaguchi
In summary: A scenario with the gravitino as LSP with a mass in the range
5-300 GeV, and a small amount of R-parity violation, 10−14 <∼ λ, λ′ <∼ 10−7,
provides a good candidate for dark matter and provides a consistent thermalhistory of the Universe (allows leptogenesis and successful BBN).
The gravitino is still undetectable in direct dark matter searches. But the R-parity
violating decay of the gravitino into photons, positrons, antiprotons and neutrinosopens the possibility of the indirect detection.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.11/33
DATA!Gamma rays
Gravitinos with a mass of several GeV decay producing photons in theGeV range −→ gamma rays.
EGRET measured gamma rays with energies between 30 MeV and 100 GeV.
The first analysis from Sreekumar et al. gave an extragalactic fluxdescribed by the power law
E2 dJdE = 1.37 × 10−6
(E
1 GeV
)−0.1
(cm2str s)−1GeV, for 50 MeV<∼ E <∼ 10 GeV
Close to the prediction for the γ- ray flux from gravitino decay when λ ≃ 10−7!!
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.12/33
The more recent analysis by Strong, Moskalenko and Reimer (’04) shows a power law
behaviour between 50 MeV and 2 GeV, but a clear excess between 2 GeV and 50GeV!!
10-1 100 101 102 103 104 105 106 107 108 109
Photon Energy (keV)
0.1
1.0
10.0
100.0
E2 d
J/dE
(ke
V2 /(
cm2 -s
-keV
-sr)
HEAO A2,A4(LED)
ASCA HEAO-A4 (MED)
COMPTEL
v
EGRET
The photon flux from the decay of gravitinos may be hidden in this excess.
Still, many open questions:
⋆ Extraction of the signal from the galactic foreground
⋆ Is the signal isotropic/anisotropic?
⋆ Precise shape of the energy spectrum?
GLAST will clarify these issues.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.13/33
Positrons
The HEAT collaboration has reported an excess of positrons at energies >∼ 7 GeV.
Same energies as the EGRET excess!
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Background only
HEAT 94/95/00
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.14/33
Positrons
The HEAT collaboration has reported an excess of positrons at energies >∼ 7 GeV.
Same energies as the EGRET excess!
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
PAMELA will provide an accurate measurement of the positron fraction.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.14/33
Antiprotons
10-3
10-2
10-1
10-1
1 10
Kinetic Energy (GeV)
p– fl
ux (
m-2
sr-1
sec-1
GeV
-1)
1
1
Bottino2
2
Bergstrom3
3
Biebar4
4Mitsui λ(R,β)
55
Mitsui λ(R)
BESS(95+97)BESS(93)IMAXCAPRICE
Cosmic Ray P–
The antiproton flux is consistent with the astrophysical mod els
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.15/33
Gravitino decay channelsψ3/2
γ
γν
Light gravitino m3/2 <∼MW
ψ3/2 → γν
Γ(ψ3/2 → γν) =1
32π|Uγν |2
m33/2
M2P
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.16/33
Gravitino decay channelsψ3/2
γ
γν
ψ3/2
Z
Z
ν
ψ3/2
W
W
l
Light gravitino m3/2 <∼MW
ψ3/2 → γν
Γ(ψ3/2 → γν) =1
32π|Uγν |2
m33/2
M2P
“not-so-light” gravitino 100 GeV <∼m3/2 <∼ 300 GeV
ψ3/2 → Z0ν
Γ(ψ3/2 → Z0ν) =1
32π|UZν |
2m33/2
M2P
f
M2Z
m23/2
!
ψ3/2 →W±ℓ∓
Γ(ψ3/2 →W±ℓ∓) =2
32π|UWℓ|
2m3
3/2
M2P
f
M2W
m23/2
!
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.16/33
Gravitino decay channelsψ3/2
γ
γν
ψ3/2
Z
Z
ν
ψ3/2
W
W
l
γ’s
γ’s
Light gravitino m3/2 <∼MW
ψ3/2 → γν
Γ(ψ3/2 → γν) =1
32π|Uγν |2
m33/2
M2P
“not-so-light” gravitino 100 GeV <∼m3/2 <∼ 300 GeV
ψ3/2 → Z0ν
Γ(ψ3/2 → Z0ν) =1
32π|UZν |
2m33/2
M2P
f
M2Z
m23/2
!
ψ3/2 →W±ℓ∓
Γ(ψ3/2 →W±ℓ∓) =2
32π|UWℓ|
2m3
3/2
M2P
f
M2W
m23/2
!
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.16/33
Gamma-ray flux from gravitino decayThe energy spectrum of photons from gravitino decay is
dNγ
dE≃ BR(ψ3/2 → γν) δ
“
E −m3/2
2
”
+ BR(ψ3/2 →Wℓ)dNW
γ
dE+ BR(ψ3/2 → Z0ν)
dNZγ
dE
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.17/33
Gamma-ray flux from gravitino decayThe energy spectrum of photons from gravitino decay is
dNγ
dE≃ BR(ψ3/2 → γν) δ
“
E −m3/2
2
”
+ BR(ψ3/2 →Wℓ)dNW
γ
dE+ BR(ψ3/2 → Z0ν)
dNZγ
dE
The branching ratios are determined by the relative size of the mixing parameters
|Ueγν | ≃»(M2 −M1)sW cWM1c2W +M2s2W
–|U eZν |
|UfWℓ| ≃√
2cWM1s
2W +M2c
2W
M2|U eZν |
Assuming gaugino mass universality at the Grand Unified Scale,
|Ueγν | : |U eZν | : |UfWℓ| ≃ 1 : 3.2 : 3.5
m3/2 BR(ψ3/2 → γν) BR(ψ3/2 → Wℓ) BR(ψ3/2 → Z0ν)
10 GeV 1 0 0
85 GeV 0.66 0.34 0
100 GeV 0.16 0.76 0.08
150 GeV 0.05 0.71 0.24
250 GeV 0.03 0.69 0.28
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.17/33
Gamma-ray flux from gravitino decayThe energy spectrum of photons from gravitino decay is
dNγ
dE≃ BR(ψ3/2 → γν) δ
“
E −m3/2
2
”
+ BR(ψ3/2 →Wℓ)dNW
γ
dE+ BR(ψ3/2 → Z0ν)
dNZγ
dE
0.01 0.1 1 10 100E (GeV)
0.01
0.1
1
10
E2 dN
/dE
m3/2
=10 GeV
γ
0.01 0.1 1 10 100E (GeV)
0.01
0.1
1
10
E2 d
N/d
E
m3/2
=150 GeV
W
Zγ
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.17/33
Gamma ray spectrumIf gravitinos decay, we expect a diffuse background of gamma rays withtwo different sources.
The decay at cosmological distances gives rise to a perfectly isotropic
extragalactic diffuse gamma-ray flux.The decay of the gravitinos in the Milky Way halo gives rise to an anisotropic γray flux
The precise value of the flux depends on the halo profile. Averaging over allsky, one finds typically Dγ/Cγ ∼ O(1) −→ the halo contribution dominates
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.18/33
Gamma ray spectrumIf gravitinos decay, we expect a diffuse background of gamma rays withtwo different sources.
The decay at cosmological distances gives rise to a perfectly isotropic
extragalactic diffuse gamma-ray flux.The decay of the gravitinos in the Milky Way halo gives rise to an anisotropic γray flux
The precise value of the flux depends on the halo profile. Averaging over allsky, one finds typically Dγ/Cγ ∼ O(1) −→ the halo contribution dominates
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.18/33
γ ray spectrum for light gravitinos m3/2 <∼MW
Bertone, Buchmüller, Covi, AI
10-7
10-6
0.1 1 10
E2 d
J/d
E (
GeV
(cm
2 s
str
)-1)
E (GeV)
energy resolutionof EGRET: 15%
extgal
halo
m3/2 = 10 GeV, τ3/2 = 1027 s
The energy spectrum from gravitino decay is just a delta function: dNγ
dE= δ
“
E −m3/2
2
”
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.19/33
γ ray spectrum for “not-so-light” gravitinos 100 GeV <∼m3/2 <∼ 300 GeV
The total flux receives contribution from different sources.
AI, Tran
|Ueγν | : |U eZν| : |UfWℓ
| ≃ 1 : 3.2 : 3.5
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.20/33
γ ray spectrum for “not-so-light” gravitinos 100 GeV <∼m3/2 <∼ 300 GeV
The total flux receives contribution from different sources.
AI, Tran
|Ueγν | : |U eZν| : |UfWℓ
| ≃ 1 : 3.2 : 3.5
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
W -halo
W -extgal
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.20/33
γ ray spectrum for “not-so-light” gravitinos 100 GeV <∼m3/2 <∼ 300 GeV
The total flux receives contribution from different sources.
AI, Tran
|Ueγν | : |U eZν| : |UfWℓ
| ≃ 1 : 3.2 : 3.5
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
Z-halo
Z-extgal
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.20/33
γ ray spectrum for “not-so-light” gravitinos 100 GeV <∼m3/2 <∼ 300 GeV
The total flux receives contribution from different sources.
AI, Tran
|Ueγν | : |U eZν| : |UfWℓ
| ≃ 1 : 3.2 : 3.5
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
γ-halo
γ-extgal
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.20/33
γ ray spectrum for “not-so-light” gravitinos 100 GeV <∼m3/2 <∼ 300 GeV
The total flux receives contribution from different sources.
AI, Tran
|Ueγν | : |U eZν| : |UfWℓ
| ≃ 1 : 3.2 : 3.5
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
background
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.20/33
γ ray spectrum for “not-so-light” gravitinos 100 GeV <∼m3/2 <∼ 300 GeV
The total flux receives contribution from different sources.
AI, Tran
|Ueγν | : |U eZν| : |UfWℓ
| ≃ 1 : 3.2 : 3.5
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
total
τ3/2 = 1.3 × 1026s =⇒ |Ueγν | ≃ 2 × 10−10
See also talk by Koji Ishiwata
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.20/33
Positron fractionThe fragmentation of the W and Z bosons produces positrons.
The positrons travel under the influence of the tangled magnetic field ofthe galaxy and lose energy −→ Complicated propagation equation
The computation of the positron fraction requires inputs from particlephysics and from astrophysics. The EGRET anomaly fixes m3/2 ≃ 150
GeV and τ3/2 ≃ 1.3 × 1026s −→ no uncertainties from particle physics.However, there are many uncertainties from astrophysics: halo model?propagation model?
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.21/33
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.22/33
Fix M2 propagation model. Different halo models
AI, Tran
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Background only
Isothermal
NFW
Moore et al.
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.22/33
Fix M2 propagation model. Different halo models
AI, Tran
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Isothermal
Moore et al.
NFW
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
The scenario of decaying gravitino dark matter predicts a bump
in the right energy range, independently of the halo model
See also talk by Koji Ishiwata
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.22/33
AI, Tran
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
M1, MED
M2
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
Fix NFW halo model. Different propagation model
The scenario of decaying gravitino dark matter predicts a bump
in the right energy range, independently of the propagation model
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.23/33
An intriguing coincidence...The anomalies in the extragalactic gamma-ray flux and in the positronfraction can be simultaneously explained in this framework.
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Isothermal
Moore et al.
NFW
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
⋆ Recall that the scenario of decaying gravitino dark matter was initially proposednot to explain these anomalies, but to reconcile the paradigms of SUSY dark
matter, leptogenesis and BBN!⋆ This result also applies to any scenario of decaying dark matter with lifetime
∼ 1026 s which decays predominantly into Z0 or W± with momentum ∼ 50 GeV.Alejandro Ibarra (DESY) Gravitino Dark Matter – p.24/33
Antiproton fluxPropagation mechanism more complicated than for the positrons. Weneglect in our analysis reacceleration and tertiary contributions.
The predicted flux suffers from huge uncertainties due to degeneraciesin the determination of the propagation parameters.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.25/33
Antiproton fluxPropagation mechanism more complicated than for the positrons. Weneglect in our analysis reacceleration and tertiary contributions.
The predicted flux suffers from huge uncertainties due to degeneraciesin the determination of the propagation parameters.
m3/2 ≃ 150 GeV and τ3/2 ≃ 1.3 × 1026s. NFW halo model
AI, Tran
10-4
10-3
10-2
10-1
100
101
0.1 1 10 100
Ant
ipro
ton
flux
[GeV
-1 m
-2 s
-1 s
r-1]
T [GeV]
MIN
MED
MAX
Φ = 500 MV
BESS 95+97BESS 95IMAX 92
CAPRICE 94CAPRICE 98
The MAX and MED model are probably excluded (despite the uncertainties)
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.25/33
The MIN case:m3/2 ≃ 150 GeV and τ3/2 ≃ 1.3 × 1026s. NFW halo model
AI, Tran
10-3
10-2
10-1
100
0.1 1 10
Ant
ipro
ton
flux
[GeV
-1 m
-2 s
-1 s
r-1]
T [GeV]
Signal
BackgroundTotal
Φ = 500 MV
BESS 95+97BESS 95IMAX 92
CAPRICE 94CAPRICE 98
Together with the background, the total flux is a factor ∼ 2 too large
In the view of all the uncertainties in the propagation, it might bepremature to rule out the scenario of decaying gravitino dark matter onthe basis of this small excess.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.26/33
Wish listWhat will make me believe in decaying gravitino dark matter
1– No positive signal from direct dark matter search experiments.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.27/33
Wish listWhat will make me believe in decaying gravitino dark matter
1– No positive signal from direct dark matter search experiments.
2– GLAST confirms the EGRET anomaly in the extragalactic gamma rayflux.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.27/33
Wish listWhat will make me believe in decaying gravitino dark matter
1– No positive signal from direct dark matter search experiments.
2– GLAST confirms the EGRET anomaly in the extragalactic gamma rayflux.
3– The angular distribution of gamma raysat 1 GeV <
∼E <
∼100 GeV is consistent with
decaying gravitino dark matter.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.27/33
Wish listWhat will make me believe in decaying gravitino dark matter
1– No positive signal from direct dark matter search experiments.
2– GLAST confirms the EGRET anomaly in the extragalactic gamma rayflux.
3– The angular distribution of gamma raysat 1 GeV <
∼E <
∼100 GeV is consistent with
decaying gravitino dark matter.
4– The energy spectrum of gamma rays isconsistent with decaying gravitino dark matter−→ m
(γ)3/2, τ (γ)
3/2.10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.27/33
5– PAMELA confirms the anomaly in the positron fraction.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.28/33
5– PAMELA confirms the anomaly in the positron fraction.
6– The positron fraction as a function of thepositron energy is consistent with decaying
gravitino dark matter. −→ m(e+)3/2 , τ (e+)
3/2
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Isothermal
Moore et al.
NFW
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.28/33
5– PAMELA confirms the anomaly in the positron fraction.
6– The positron fraction as a function of thepositron energy is consistent with decaying
gravitino dark matter. −→ m(e+)3/2 , τ (e+)
3/2
0.01
0.1
1 10 100 1000
Pos
itron
frac
tion
e+/(
e++
e− )
T [GeV]
Isothermal
Moore et al.
NFW
Background only
HEAT 94/95/00AMS-01 98
CAPRICE 94MASS 91
7– m(γ)3/2 ≃ m
(e+)3/2
τ(γ)3/2 ≃ τ
(e+)3/2 .
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.28/33
8– Low energy supersymmetry is discovered at the LHC.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.29/33
8– Low energy supersymmetry is discovered at the LHC.9– If the stau is the NLSP, the main decay is τR → τ νµ, µ ντ (through λLLec)
cτlepτ ∼ 15 cm
(mτ
400GeV
)−1 (
λ323
10−8
)−2
Long heavily ionizing charged track followed by a muon track or a jet.A very spectacular signal at colliders!The determination of the R-parity violating coupling would lead to arelation of the gravitino lifetime and the gravitino mass:
τ3/2 ∼ 1026s( m3/2
150GeV
)−3 (
meτ
400GeV
) (τeτ
10−8s
)
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.29/33
Gamma rays as a thermometer of the Universe?If the scenario of decaying dark matter turns out to be correct, there mightbe a chance of measuring the temperature of the early Universe.
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
m3/2/2
The thermal relic abundance of gravitinos is given by
Ω3/2h2≃ 0.27
(TR
1010 GeV
)(100 GeV
m3/2
) ( meg
1 TeV
)2
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.30/33
Gamma rays as a thermometer of the Universe?If the scenario of decaying dark matter turns out to be correct, there mightbe a chance of measuring the temperature of the early Universe.
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
m3/2/2
If there is only thermal production
TR ≃ 2 × 1010GeV
(Ω3/2h
2
0.1
) ( m3/2
150GeV
) ( meg
500 GeV
)−2
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.30/33
Gamma rays as a thermometer of the Universe?If the scenario of decaying dark matter turns out to be correct, there mightbe a chance of measuring the temperature of the early Universe.
10-7
10-6
0.1 1 10 100
E2 d
J/dE
[GeV
cm
-2 s
-1 s
r-1]
E [GeV]
Gamma-ray spectrum for m3/2 = 150 GeV
m3/2/2
In general
TR <∼
2 × 1010GeV
(Ω3/2h
2
0.1
)( m3/2
150GeV
)( meg
500 GeV
)−2
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.30/33
ConclusionsGravitino dark matter is a very interesting scenario.
Gravitino dark matter with R-parity violation is even more interesting.The potential conflict of BBN and leptogenesis is automatically solved,while preserving the nice features of the gravitino as dark matter. Also,indirect detection might be possible!
The anomalies observed in the extragalactic gamma-ray flux (EGRET)and the positron fraction (HEAT) can be simultaneously explained bythe decay of the gravitino.
Future experiments (GLAST, PAMELA, LHC, XENON, CDMS...) willprovide in the near future indications for this scenario or evidencesagainst it.
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.31/33
Isotropy of the signal
energy (MeV) 10 210 310 410 510
MeV
-1
s-1
sr
-2. i
nten
sity
, cm
2E
-310
V Strong, Moskalenko, Reimer
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.32/33
l b Intensity 0.1-10 GeV Description
0–360 < −10, > +10 11.10 ± 0.12 N+S hemispheres
0–360 < −10 11.70 ± 0.15 N hemisphere
0–360 > +10 9.28 ± 0.21 S hemisphere
270–90 < −10, > +10 11.90 ± 0.17 Inner Galaxy N+S
90–270 < −10, > +10 9.75 ± 0.17 Outer Galaxy N+S
0–180 < −10, > +10 10.80 ± 0.17 Positive longitudes N+S
180–360 < −10, > +10 11.60 ± 0.16 Negative longitude N+S
270–90 > +10 13.00 ± 0.22 Inner Galaxy N
270–90 < −10 9.14 ± 0.32 Inner Galaxy S
90–270 > +10 10.60 ± 0.22 Outer Galaxy N
90–270 < −10 8.18 ± 0.34 Outer Galaxy S
Alejandro Ibarra (DESY) Gravitino Dark Matter – p.33/33