We don ’t know it, because we don’t see it!

W. de Boer, Univ. Karlsruhe

Heidelberg, July 11, 2006 1

We don’t know it,because we don’t see it!

Indirect Evidence for Dark Matter from Galactic 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, A&A, 444 (2005) 51

DM what is it?



Do we have Dark Matter in our Galaxy?

RotationcurveSolarsystem

rotation curveMilky Way



How much Dark Matter in Universe?

If it is not dark, it does not matter

Dark Matter: Grav. attractiveDark Energy: Grav. repulsive (if dρ/dt=0!)= ρ / ρcrit = B+ DM + =123±4% of energy in Universe= DM (WIMPS)

SNIa sensitive toacceleration, i.e. - (SM+ DM)

CMB sensitive tooverall density, i.e. + SM + DM)



Expansion rate of universe determines WIMP annihilation cross section

Thermal equilibrium abundance

Actual abundance

T=M/22Co

mo

vin

g n

um

ber

d

ensi

ty

x=m/TJungmann,Kamionkowski, Griest, PR 1995

WMAP -> h2=0.1130.009 -> <v>=2.10-26 cm3/s

DM increases in Galaxies:1 WIMP/coffee cup 105 <ρ>. DMA (ρ2) restarts again..

T>>M: f+f->M+M; M+M->f+fT<M: M+M->f+fT=M/22: M decoupled, stable density(wenn Annihilationrate Expansions- rate, i.e. =<v>n(xfr) H(xfr) !)

Annihilation into lighter particles, likeQuarks and Leptons -> 0’s -> Gammas!Only assumption in this analysis:WIMP = THERMAL RELIC!



Example of DM annihilation (SUSY)

Dominant + A b bbar quark pairSum of diagrams should yield<σv>=2.10-26 cm3/s to getcorrect relic density

Quark-Fragmentation known!Hence spectra of positrons,gammas and antiprotons known!Relative amount of ,p,e+ known as well.

f

f

f

f

f

f

Z

Z

W

W 0

f~

A Z

≈37 gammas



Idea of analysis

Wd

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C.

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Kazakov,

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508617,

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444 (

2005)

51

Idea:

Thermal relics disappeared by annihilation.(From WMAP Annihilation cross section <σv>=2.10-27/Ωh2)

Annihilation into Quarks with this x-section should yieldlarge amount of Gamma Rays (37γ’s/Annihilation from LEP data)

Gamma spectrum from DMA significantly harder than dominantbackground 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 withexpected spectral SHAPE IN ALL SKY directions andINTENSITY of excess allows to measure DM distributionin GALAXY. Then one knows MASS distribution of DM andvisible matter and can calculate ROTATION CURVE (RC).

IF GAMMA RAYS indeed originate from DMA, then thiscan be proven by calculating shape of RC from Gamma Rays!



Instrumental parameters:

Energy range: 0.02-30 GeVEnergy resolution: ~20%Effective area: 1500 cm2

Angular resol.: <0.50

Data taking: 1991-1994Main results: Catalogue of point sourcesExcess in diffuse gamma rays

This talk:Excess consistent with DMA of 60 GeV WIMP in ALL skydirectionsExcess distribution explainspeculiar shape of rotation curve

(A&A, 444 (2005) 51)

EGRET on CGRO (Compton Gamma Ray Observ.)

Data publicly available from NASA archive



The EGRET excess of diffuse galactic gamma rays without and with DM annihilation

π0π0

WIM

PS

IC

Brems

IC

Brems

If normalization free, only relative point-to-point errors of ≤7% important, not absolute normalization error of 15%. Statistical errors negligible.

Fit only KNOWN shapes of BG + DMA, i.e. 1 or 2 parameter fitNO GALACTIC models needed. Propagation of gammas straightforward



No SM

Electrons

No SM

Protons

Quarks fromWIMPS

Quarks in protons

What about background shape?

Background from nuclear interactions (mainly p+p-> π0 + X -> + X inverse Compton scattering (e-+ -> e- + ) Bremsstrahlung (e- + N -> e- + + N)Shape of background KNOWN if Cosmic Ray spectra of p and e- known



PYTHIA processes: 11 f+f' -> f+f' (QCD) 2370 12 f+fbar -> f'+fbar' 0 13 f+fbar -> g + g 0 28 f+g -> f + g 213068 g+g -> g + g 151053 g+g -> f + fbar 20 92 Single diffractive (XB) 1670 93 Single diffractive (AX) 1600 94 Double diffractive 70095 Low-pT scattering 0Prompt photon production:14 f+fbar -> g+γ 018 f+fbar -> γ +γ 029 f+g -> f +γ 1115 g+g -> g + γ 0114 g+g -> γ + γ 0

Contribution from various hadronic processes

2 GeV4

816

3264

diff.



Background + signal describe EGRET data!

Blue: background uncertainty

Background + DMA signal describe EGRET data!

Blue: WI MP mass uncertainty

50 GeV

70

I CI C



Analysis of EGRET Data in 6 sky directions

A: inner Galaxy (l=±300, |b|<50)B: Galactic plane avoiding AC: Outer Galaxy

D: low latitude (10-200)

E: intermediate lat. (20-600)F: Galactic poles (60-900)

A: inner Galaxy B: outer disc C: outer Galaxy

D: low latitude E: intermediate lat. F: galactic poles

Total 2 for all regions :28/36 Prob.= 0.8 Excess above background > 10σ.



Fits for 180 instead of 6 regions

180 regions:80 in longitude 45 bins4 bins in latitude 00<|b|<50 50<|b|<100

100<|b|<200

200<|b|<900

4x45=180 bins

bulge disk

sun



x y

z

2002,Newberg et al. Ibata et al, Crane et al. Yanny et al.

1/r2 profile and ringsdetermined from inde-pendent directions

xy

xz

Expected Profile

v2M/r=cons.and

(M/r)/r2

1/r2

for const.rotation

curveDivergent for

r=0?NFW1/r

Isotherm const.

Dark Matter distribution

Halo profile

Observed Profile

xy

xz

Outer Ring

Inner Ring

bulge

tota

lDM

1/r2 halodisk

Rotation Curve

Normalize to solar velocity of 220 km/s



Honma & Sofue (97)Schneider &Terzian (83)Brand & Blitz(93)

Rotation curve of Milky Way



Do other galaxies have bumps in rotation curves?

Sofue & Honma



Possible origin of ring like structure

Infall of dwarf galaxy in gravitational potential of larger galaxyinto elliptical orbit start precessions, if matter is notdistributed homogeneous.

Tidal forces gradient of field, i.e. 1/r3. This meanstidal disruption only effective at pericenter for large ellipticity!

Apocenter

Pericenter

Could tidal disruption of dwarf galaxy lead to ringlike structure of 1010 solar masses?

N-body simulations no clearanswer. All depends oninitial conditions. Also no clear explanation for ring ofstars of 109 solar masses.



Tidal disruption of satellite in potential of larger galaxy

Hayashi et al.,astro-ph/02003004



Enhancement of inner (outer) ring over 1/r2 profile 6 (8).Mass in rings 0.3 (3)% of total DM

Inner Ring coincides with ring of dust and H2 -> gravitational potential well!

H2

4 kpc coincides with ring ofneutral hydrogen molecules!H+H->H2 in presence of dust->grav. potential well at 4-5 kpc.



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 substructure

A: DM annihilation

A: standard profile + substructure

A: Cross sections perfectly consistent with mSUGRA for light gauginos, heavy squarks/sleptons



10 (wrong) objections against DMA interpretation

1) 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.



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):1) 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 -> DMA fills up box with high density of antiprotons2) More realistic models have anisotropic diffusion. E.g. spiral galaxies have magnetic fields perpendicular to disk-> antiprotons may spiral quickly out of Galaxy.


4) Does antiproton rate exclude interpretation of EGRET data? (L.B.)



Magnetic fields observed in spiral galaxies

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 -> anisotropic diffusion

disk

fieldline



Antiprotons B/C ratio

Preliminary results from GALPROP with isotropic and anisotropic propagation

Summary: with anisotropic propagation you can send charged particleswhereever you want and still be consistent with B/C and 10Be/9Be



Cosmic clocks: 10Be/9Be




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.

R0=8.3 kpc

R0=7.0v

R/R0

Innerrotationcurve

Outer RC

Black hole at centre: R0=8.00.4 kpc

Sofue &Honma

Statistical errors only

EGRET EXCESS




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).



What

about

Supersymmetry?



Symmetry between

Fermions Bosons(Matter particles) (exchange particles)

Comparison with SUPERSYMMETRY

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



EGRET?

Cross sections for Direct DM detection in mSUGRA



Gauge unification perfect with SUSY spectrum from EGRET

With SUSY spectrum from EGRET + WMAP data and start values of couplings from final LEP data perfect gauge coupling unification!

Up

date

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dB

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SM SUSY

Also b->s and g-2 in agreement with SUSY spectrum from EGRET



Summary

EGRET excess shows that

WIMP is thermal relic with expected annihilation into quark pairs

SPATIAL DISTRIBUTION of annihilation signal is signature for DMAwhich clearly shows that EGRET excess is tracer of DM by fact thatone can CONSTRUCT ROTATION CURVE FROM GAMMA RAYS.

DM becomes visible by gamma rays from fragmentation(30-40 gamma rays of few GeV pro annihilation from π0 decays)

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, ….

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.

We don ’t know it, because we don’t see it!

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