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Indirect Evidence for Dark Matter from Galactic
Gamma Rays
DM what is it?
We dont know it, because we dont see it!
WdB, C. Sander, V. Zhukov, A. Gladyshev, D.
Kazakov, EGRET excess of diffuse Galactic Gamma
Rays as Tracer of DM, astro-ph/0508617, AA, 444
(2005) 51
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Do we have Dark Matter in our Galaxy?
Rotationcurve Solarsystem
rotation curve Milky Way
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How much Dark Matter in Universe?
If it is not dark, it does not matter
SNIa sensitive to acceleration, i.e. ?? - (?SM
?DM)
Dark Matter Grav. attractive Dark Energy Grav.
repulsive (if d?/dt0!) ? ? /
?crit ?B ?DM ??1 234 of energy in
Universe DM (WIMPS)
CMB sensitive to overall density, i.e. ?? ?SM
?DM)
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Expansion rate of universe determines WIMP
annihilation cross section
Thermal equilibrium abundance
Actual abundance
Comoving number density
WMAP -gt ?h20.113?0.009 -gt
lt?vgt2.10-26 cm3/s
DM increases in Galaxies ?1 WIMP/coffee cup ?105
lt?gt. DMA (??2) restarts again..
Annihilation into lighter particles, like Quarks
and Leptons -gt ?0s -gt Gammas!
TM/22
Only assumption in this analysis WIMP THERMAL
RELIC!
xm/T
Jungmann,Kamionkowski, Griest, PR 1995
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Example of DM annihilation (SUSY)
37 gammas
Quark-Fragmentation known! Hence spectra of
positrons, gammas and antiprotons known! Relative
amount of ?,p,e known as well.
Dominant ? ? ? A ? b bbar quark pair Sum of
diagrams should yield ltsvgt2.10-26 cm3/s to
get correct relic density
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Idea of analysis
Idea Thermal relics disappeared by
annihilation. (From WMAP Annihilation cross
section ltsvgt2.10-27/Oh2) Annihilation into
Quarks with this x-section should yield large
amount of Gamma Rays (37?s/Annihilation from LEP
data) Gamma spectrum from DMA significantly
harder than dominant background from inelastic pp
collisions (Cosmic Rays on H-gas) Background
shape KNOWN from fixed target experiments, DMA
Gamma Ray shape KNOWN from LEP data EGRET Data
indeed shows such an expected excess
with expected spectral SHAPE IN ALL SKY
directions and INTENSITY of excess allows to
measure DM distribution in GALAXY. Then one knows
MASS distribution of DM and visible matter and
can calculate ROTATION CURVE (RC). IF GAMMA RAYS
indeed originate from DMA, then this can be
proven by calculating shape of RC from Gamma Rays!
WdB, C. Sander, V. Zhukov, A. Gladyshev, D.
Kazakov, EGRET excess of diffuse Galactic Gamma
Rays as Tracer of DM, astro-ph/0508617, AA, 444
(2005) 51
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EGRET on CGRO (Compton Gamma Ray Observ.)Data
publicly available from NASA archive
Instrumental parameters Energy range 0.02-30
GeV Energy resolution 20 Effective area 1500
cm2 Angular resol. lt0.50 Data taking 1991-1994
Main results Catalogue of point sources Excess
in diffuse gamma rays
This talk Excess consistent with DMA of 60 GeV
WIMP in ALL sky directions Excess distribution
explains peculiar shape of rotation curve
(AA, 444 (2005) 51)
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The EGRET excess of diffuse galactic gamma rays
without and with DM annihilation
Fit only KNOWN shapes of BG DMA, i.e. 1 or 2
parameter fit NO GALACTIC models needed.
Propagation of gammas straightforward
If normalization free, only relative
point-to-point errors of 7 important, not
absolute normalization error of 15. Statistical
errors negligible.
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What about background shape?
No SM
No SM
Protons
Electrons
Background from nuclear interactions (mainly
pp-gt p0 X -gt ? X inverse
Compton scattering (e- ? -gt e- ?)
Bremsstrahlung (e- N -gt e- ?
N) Shape of background KNOWN if Cosmic Ray
spectra of p and e- known
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Contribution from various hadronic processes
PYTHIA processes 11 ff' -gt ff' (QCD)
2370 12 ffbar -gt f'fbar' 0
13 ffbar -gt g g 0
28 fg -gt f g 2130 68 gg
-gt g g 1510 53 gg -gt f fbar
20 92 Single diffractive (XB)
1670 93 Single diffractive (AX) 1600 94
Double diffractive 700 95 Low-pT
scattering 0 Prompt photon
production 14 ffbar -gt g? 0 18
ffbar -gt ? ? 0 29 fg -gt f ?
1 115 gg -gt g ?
0 114 gg -gt ? ? 0
2 GeV
4
8
16
32
64
diff.
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Background signal describe EGRET data!
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Analysis of EGRET Data in 6 sky directions
C outer Galaxy
A inner Galaxy
B outer disc
Total ?2 for all regions 28/36 ? Prob. 0.8
Excess above background gt 10s.
E intermediate lat.
F galactic poles
D low latitude
A inner Galaxy (l300, blt50) B Galactic
plane avoiding A C Outer Galaxy
D low latitude (10-200) E intermediate lat.
(20-600) F Galactic poles (60-900)
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Fits for 180 instead of 6 regions
180 regions 80 in longitude ? 45 bins 4 bins in
latitude ? 00ltblt50 50ltblt100
100ltblt200 200ltblt900 ? 4x45180 bins
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Dark Matter distribution
v2?M/rcons. and ??(M/r)/r2 ??1/r2 for
const. rotation curve Divergent
for r0? NFW?1/r Isotherm const.
Halo profile
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Rotation curve of Milky Way
Honma Sofue (97) Schneider Terzian (83) Brand
Blitz(93)
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Do other galaxies have bumps in rotation curves?
Sofue Honma
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Possible origin of ring like structure
Infall of dwarf galaxy in gravitational potential
of larger galaxy into elliptical orbit start
precessions, if matter is not distributed
homogeneous. Tidal forces ? gradient of field,
i.e. ? 1/r3. This means tidal disruption only
effective at pericenter for large ellipticity!
Could tidal disruption of dwarf galaxy lead to
ringlike structure of 1010 solar masses? N-body
simulations no clear answer. All depends
on initial conditions. Also no clear explanation
for ring of stars of 109 solar masses.
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Tidal disruption of satellite in potential of
larger galaxy
Hayashi et al., astro-ph/02003004
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Inner Ring coincides with ring of dust and H2 -gt
gravitational potential well!
4 kpc coincides with ring of neutral hydrogen
molecules! HH-gtH2 in presence of dust-gt grav.
potential well at 4-5 kpc.
Enhancement of inner (outer) ring over 1/r2
profile 6 (8). Mass in rings 0.3 (3) of total DM
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7 Physics Questions answered SIMULTANEOUSLY if
WIMP thermal relic

• Astrophysicists
• What is the origin of GeV excess of diffuse
  Galactic Gamma Rays?
• Astronomers
• Why a change of slope in the galactic rotation
  curve at R0 11 kpc?
• Why ring of stars at 14 kpc?
• Why ring of molecular hydrogen at 4 kpc?
• Cosmologists How is DM annihilating?A into
  quark pairs
• How is Cold Dark Matter distributed?
• Particle physicists
• Is DM annihilating as expected in
  Supersymmetry?

A DM annihilation
A DM substructure
A standard profile substructure
A Cross sections perfectly consistent with
mSUGRA for light gauginos, heavy squarks/sleptons
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10 (wrong) objections against DMA interpretation

• Proton spectra only measured locally. Spectra
  near center of
• galaxy, where protons are accelerated, can be
  different and
• produce harder gamma spectrum, as observed by
  EGRET.

Answer proton energy loss times larger than age
of universe, so proton energy spectra
will become equal by diffusion This is
PROVEN by the fact that we see same spectrum
and same excess in inner and outer galaxy.
2) Is background known well enough to make such
strong statements?
A Background SHAPE is known, since mainly from
pp collisions. Analysis does not depend on
absolute fluxes from propagation models.
Propagation.of gammas is straightforward.
3) Can unresolved point sources be responsible
for excess?
Answer NO, if they have similar spectra as the
many resolved point sources, they would
reduce the data points at low energy,
thus increasing the DMA contribution if shapes
are fitted. Also do not expect 1/r2
profile for point sources.
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10 (wrong) objections against DMA interpretation
4) Does antiproton rate exclude interpretation of
EGRET data? (L.B.)
Bergstrom et al. astro-ph/0603632, Abstract we
investigate the viability of the model using the
DarkSUSY package to compute the gamma-ray and
antiproton fluxes. We are able to show that their
(WdB et al) model is excluded by a wide margin
from the measured flux of antiprotons.

• Problem with DarkSUSY (DS)
• Flux of antiprotons/gamma in DarkSUSY ?O(1) from
  DMA.
• However, O(10-3) from LEP data
• Reason DS has diffusion box with isotropic
  diffusion -gt
• DMA fills up box with high density
  of antiprotons
• 2) More realistic models have anisotropic
  diffusion.
• E.g. spiral galaxies have magnetic fields
  perpendicular to
• disk-gt antiprotons may spiral quickly out of
  Galaxy.

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Magnetic fields observed in spiral galaxies
fieldline
disk
A few uG perpendicular to disc Diffusion
preferentially?? to disc? Alternativ strong
convection
A few µG along spiral arms Can lead to slow
radial diffusion
Isotropic diffusion assumes randomly oriented
magnetic turbulences. Preferred magnetic field
directions -gt anisotropic diffusion
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Preliminary results from GALPROP with isotropic
and anisotropic propagation
Antiprotons
B/C ratio
Summary with anisotropic propagation you can
send charged particles whereever you want and
still be consistent with B/C and 10Be/9Be
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Cosmic clocks 10Be/9Be
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10 (wrong) objections against DMA interpretation
5) Rotation curves in outer galaxy measured with
different method than inner rotation curve.
Can you combine? Also it depends on R0.
Answer first points of outer RC have same
negative slope as inner RC so no
problem with method. Change of slope seen for
every R0.
6) Ringlike structures have enhanced density of
hydrogen, so you expect excess of gamma
radiation there. Why you need DMA?
Answer since we fit only the shapes of signal
and BG, a higher gas density is
automatically taken into account and DMA is
needed to fit the spectral shape of
the data.
7) Is EGRET data reliable enough to make such
strong statements?
Answer EGRET spectrometer was calibrated in
photon beam at SLAC. Calibration
carefully monitored in space. Impossible
to get calibration wrong in such a way that it
fakes DMA.
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10 (wrong) objections against DMA interpretation
7) How can you be sure that this outer ring is
from the tidal disruption of satellite
galaxy, so one can expect DM there?
Answer one observes rings for all three
ingredients of a galaxy gas, stars
and DM. The stars cannot be part of the disk,
since the thickness of the ring is a
factor 20 larger than the thickness of
the disk. Furthermore, very small velocity
dispersion of stars
8) Is it not peculiar that the rings are in the
plane of the disk?
Answer the angular momenta of halo and disk tend
to align after a certain time of
precession, so rings end up in plane of the disk..
9) The inner ring was not observed as a ring of
stars. How can you be sure DM concentrates
there?
Answer The density of stars and dust is to high
to obtain substructure in the star
population. However, the ring of dust and
molecular hydrogen are proof of a
graviational well, which indicates DM.
10) How can one reconstruct 3D halo profiles, if
one observes gamma rays only along the line
of sight without knowing the distance?
Answer if one observes in ALL directions, one
can easily unfold, see rings of Saturn
(same problem).
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What about Supersymmetry?
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Comparison with SUPERSYMMETRY
Symmetry between
Fermions ? Bosons
(Matter particles)
(exchange particles)
SUSY masses 100 - 2000 GeV !
Lightest Supersymmetric Particle (LSP) is stable,
heavy and weakly interacting ? excellent Weakly
Interacting Massive Particle (WIMP) ? DM
candidate! R-Parity conservation TWO SUSY
particles at each vertex! LSP mostly photinolike
in MSSM ? DM supersymmetric partner of CMB
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Cross sections for Direct DM detection in mSUGRA
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Gauge unification perfect with SUSY spectrum from
EGRET
SM
SUSY
Update from Amaldi, dB, Fürstenau, PLB 260 1991
With SUSY spectrum from EGRET WMAP data and
start values of couplings from final LEP data
perfect gauge coupling unification!
Also b-gts? and g-2 in agreement with SUSY
spectrum from EGRET
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Summary
EGRET excess shows that
WIMP is thermal relic with expected annihilation
into quark pairs
DM becomes visible by gamma rays from
fragmentation (30-40 gamma rays of few GeV pro
annihilation from p0 decays)
Results rather model independent, since only
KNOWN spectral shapes of signal and background
used, NO model dependent calculations of
abs.fluxes. Different models or unknown
experimental problems may change boost factor
and/or WIMP mass, BUT NOT the distribution in the
sky.
SPATIAL DISTRIBUTION of annihilation signal is
signature for DMA which clearly shows that EGRET
excess is tracer of DM by fact that one can
CONSTRUCT ROTATION CURVE FROM GAMMA RAYS.
Conventional models CANNOT explain above points
SIMULTANEOUSLY, especially spectrum of gamma rays
in all directions, 1/r2 profile, shape of
rotation curve, ring of stars at 14 kpc and ring
of H2 at 4 kpc, .