Lars Bergstrm

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Indirect detection of dark matter
candidates through gamma-rays

• Lars Bergström
• Department of Physics
• Stockholm University
• lbe_at_physto.se

La Thuile, March 21, 2006
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WMAP Collaboration (Spergel al), 2006
Nonbaryonic Dark Matter exists!
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Which dark matter candidate is the correct one?
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• Methods of Weakly Interacting Massive Particle
  (WIMP) Dark Matter detection
• Discovery at accelerators (Fermilab, LHC,..)
• Direct detection of halo particles in
  terrestrial detectors
• Indirect detection of neutrinos, gamma rays,
  radio waves, antiprotons, positrons in earth- or
  space-based experiments

Direct detection
The basic process for indirect detection is
annihilation, e.g, neutralinos
Neutralinos are Majorana particles
Enhanced for clumpy halo near galactic centre
and in Sun Earth
Indirect detection
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Indirect detection neutralino example
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P. Gondolo, J. Edsjö, L.B., P. Ullio, Mia Schelke
and E. A. Baltz, JCAP 0407008, 2004
astro-ph/0406204
Release 4.1 includes coannihilations interface
to Isasugra New release soon!
Neutralino dark matter made easy - Can be
freely dowloaded from http//www.physto.se/edsjo/
ds
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Gamma-rays
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USA-France-Italy-Japan- Germany-Sweden
collaboration, launch 2007
GLAST can search for dark matter signals up to
300 GeV. (It is also likely to detect a few
thousand new GeV blazars )
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GLAST can cover energies up to 300 GeV. For
higher energies, Air Cherenkov Telescopes (HESS
MAGIC, VERITAS, CANGAROO) become competitive.
Example 1.4 TeV Higgsino with WMAP-compatible
relic density (L.B.,T. Bringmann, M. Eriksson and
M. Gustafsson, PRL 2005)
Intrinsic line width DE/E 10-3
New contribution (internal bremsstrahlung)
Gamma-ray spectrum seen by an ideal detector
Same spectrum seen with 15 energy resolution
(typical of ACT)
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H.E.S.S. in Namibia
Magic in Canary Islands VERITAS under
construction
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Kaluza-Klein models L.B., T. Bringmann, M.
Eriksson M. Gustafsson, PRL 2005 Mass 600 800
GeV See talk by E. Nuss later in this session
Quark fragmentation (e.g., SUSY)
From tau leptons
With internal Bremsstrahlung
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Dark matter clumps in the halo?
Stoehr, White, Springel,Tormen, Yoshida, MNRAS
2003. (Cf Calcaneo-Roldan Moore, PRD, 2000.)
Important problem What is the fate of the
smallest substructures? Berezinsky, Dokuchaev
Eroshenko, 2003, 2005 (see poster) Green,
Hofmann Schwarz, astro-ph 2003. Diemand, Moore
Stadel, 2005 The first structures to form are
mini-halos of 10-6 solar masses many of these
may survive
Milky Way simulation, Helmi, White Springel,
PRD, 2002
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INTEGRAL all-sky picture of positronium gamma
line (511 keV) emission unknown origin (J.
Knödlseder et al., 2003 - 2006)
Is it dark matter annihilation (very low mass
needed, less than 20 MeV)? Could also be
explained by Type IA supernovae, or low mass
X-ray binaries?
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Beacom and Yüksel, 2005
Inflight annihilation ? mass has to be less than
around 3 MeV!
Very difficult to find viable particle physics
models (But for some possibilities, see Boehm
and Fayet, 2004 Ascasibar talk Friday)
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W. de Boer, 2003-2005
Filled by 65 GeV neutralino annihilation
Galactic rotation curve
Data explained by 50-100 GeV neutralino?
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L.B., J. Edsjö, M. Gustafsson P. Salati, 2006

DM density concentrated to the galactic plane
Antiprotons pose a major problem for this type of
model
Expected antiproton flux from de Boers
supersymmetric models
Standard (secondary) production from cosmic rays
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Diffuse cosmic gamma-rays
EGRET points will change as GLAST resolves more
AGNs
Idea (L.B., Edsjö Ullio, 2001) Integrated
gamma-signal over all large- and small-scale
structure may give observable diffuse gamma-ray
flux for CDM-type cuspy halos and substructure.
Redshifted gamma line in favourable cases.
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Could the diffuse extragalactic gamma-ray
background be generated by neutralino
annihilations?
GeV bump? (Moskalenko, Strong, Reimer, 2004)
Steep (Moore) profile needed for DM substructure
some fine-tuning to get high annihilation rate
Elsässer Mannheim, Phys. Rev. Lett. 94171302,
2005
Energy range is optimal for GLAST!
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Problem (Ando, 2005) It is difficult to
reproduce extragalactic result of Elsässer
Mannheim, without overproducing gammas from g.c.
Resolution (Oda, Totani Nagashima, 2005)
clumpy halos tidal effects remove substructure
near centres of haloes
Effects of a clumpy halo on diffuse galactic plus
extragalactic gamma-ray signal. Satisfies bound
from gal. centre
Oda, Totani and Nagashima, 2005 cf. also Pieri,
Branchini and Hofmann, 2005
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Angular power spectrum for gamma-rays from dark
matter
Ando and Komatsu, 2005
GLAST estimated error bars (for particular DM
model)
GLAST observations will be crucial
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H.J. Völk, 2006
HESS observations of galactic center (cf also
MAGIC 2006 complete agreement both for
magnitude and slope)
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Dark matter annihilation?
Wrong mass and shape for natural models
c.f. L.B., T. Bringmann, M. Eriksson, M.
Gustafsson, 2005
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Conventional explanation, Aharonov Neronov,
2005
Prediction variability on 1-hour
timescale GLAST will fill in data between EGRET
and HESS
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Zaharijas Hooper, 2006
The HESS result means that a dark matter signal
has to be found below a large background (? the
galactic center may not be optimal for DM search)
m? 3 TeV
m? 500 GeV
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Some models exist where gamma-line from the
galactic center may be visible (but need specific
values of halo parameters)
GLAST
HESS
GLAST
HESS
??
Z?
Zaharijas Hooper, 2006
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DRACO and dark matter
Size 0.5 degrees across. Optically very
faint. Integrated magnitude 11 ? good candidate
for ACT observations.
Draco Dwarf spheroidal galaxy in the Local
Group. Estimated total mass 107 109 solar
masses luminosity 2 x 105 Lsun ? mass-to-light
ratio 100-1000. One of the most dark
matter-dominated galaxies known! Starpoor ? much
cleaner observation conditions than Gal. Center
SDSS
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Dark Matter in Draco? CACTUS solar array recent
results (TAUP Meeting 2005)
Preliminary, unpublished data Signal looks too
strong?, see N.W. Evans, F. Ferrer S.Sarkar,
2004
Talk by CACTUS Collaboration at UCLA, Feb, 2006
Data reanalyzed, no signal above 100 GeV!
L.B. D. Hooper, 2005 S. Profumo M.
Kamionkowski, 2006 Rate may be increased by
factor 10, beyond that one needs nonthermally
produced WIMPs. Tension with EGRET data ?
non-standard spectrum needed.
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• None of the above?

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Conclusions

• The existence of Nonbaryonic Dark Matter has been
  definitely established from cosmological
  measurements.
• CDM is favoured (e.g., supersymmetric particles).
• Indications of gamma-ray excess from galactic
  center, the galactic halo, the extragalactic flux
  and perhaps from the Draco dwarf galaxy. However,
  none compelling (at least to this speaker). Need
  more definitive spectral signature the gamma
  line or a sharp drop at E? mDM would be a
  smoking gun.
• Where does the GeV excess in galactic and
  extragalactic gamma-rays come from? GLAST data
  will be crucial.
• The hunt is going on many new experiments
  (GLAST, VERITAS, AMS) are coming on soon!
• Complementarity GLAST will do all-sky search for
  hot spots with high sensitivity ACTs may do
  small-angle, detailed study.
• ACTs will soon have interesting data on dwarf
  galaxies.
• LHC starts within 2 years
• The dark matter problem may be near its solution