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Excess of Diffuse Galactic Gamma Rays Interpreted as Dark Matter Annihilation

This study analyzes the excess of diffuse Galactic gamma rays observed by EGRET and interprets it as the annihilation of dark matter particles. The data is consistent with Supersymmetry and suggests a WIMP mass between 50 and 100 GeV.

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Excess of Diffuse Galactic Gamma Rays Interpreted as Dark Matter Annihilation

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  1. From CMB + SN1a + structure formation EGRET excess of diffuse Galactic Gamma Rays interpreted as Dark Matter Annihilation Wim de Boer, Christian Sander, Valery Zhukov Univ. Karlsruhe Dmitri Kazakov, Alex Gladyshev Dubna • Outline (see astro-ph/0408272) • EGRET Data on diffuse Gamma Rays show excess in all sky directions with the SAME energy spectrum from monoenergetic quarks • WIMP massbetween 50 and 100 GeV from spectrum of EGRET excess • Halo distribution from sky map • Data consistent with Supersymmetry

  2.   f f f ~ f A Z    f f f   W Z 0    Z W DM annihilation in Supersymmetry ≈ 37 gammas B-fragmentation well studied at LEP! Yield and spectra of positrons, gammas and antiprotons well known! Dominant diagram for WMAP cross section in MSSM:  +   A  b bbar quark pair Galaxy = SUPER-B-factory with luminosity some 40 orders of magnitude above man-made B-factories

  3. More precisely by solving Boltzmann eq. Basics from cosmology:Hubble const. determines WIMP annihilation x-section T>>M: f+f->M+M; M+M->f+f T<M: M+M->f+f T=M/22: M decoupled, stable density (wenn annihilation rate  expansion rate,i.e. =<v>n(xfr)  H(xfr) !) Thermal equilibrium abundance Actual abundance Comoving number density H-Term takes care of decrease in density by expansion. Right-hand side: annihilation and production. Jungmann,Kamionkowski, Griest, PR 1995 h2 = mn/c  2.10-27 [cm3/s]/<v> (<v> independ. of m!) T=M/22 Present WMAP h2=0.1130.009 requires <v>  2.10-26 cm3/s x=m/T DM density increases locally after galaxy formation. In this room: 1 WIMP/coffee cup 105 averaged density.

  4. WIMP MASS 50 - 100 GeV RED=flux from DM Annihilation Yellow = backgr. Blue = BG uncert. 65 0 WIMPS 100 0 IC WIMPS IC Extragal. Bremsstr. Extragal. Bremsstr. Basics of background and signal shapes Blue: uncertainty from WIMP mass Blue: uncertainty from background shape

  5. Quarks from WIMPS Quarks in protons Basics of background and signal shapes No SM No SM Protons Electrons

  6. Energy loss times of electrons and nuclei t-1 = 1/E dE/dt univ Protons diffuse for long times without loosing energy! If centre would have harder spectrum, then hard to explain why excess in outer galaxy has SAME shape (can be fitted with same WIMP mass!)

  7. EGRET on CGRO (Compton Gamma Ray Observ.) 9 yrs of data taken (1991-2000) Main purpose: sky map of point sources above diffuse BG.

  8. Basics of astro-particle physics Gamma Ray Flux from WIMP annihilation in given direction ψ: Similar expressions for: pp->0+x->+x, ( given by gas density, highest in disc) e->e, eN->eN, ( given by electron/gamma density, highest in disc) Extragalactic Background (isotropic) DM annihilation ( 1/r2 for flat rotation curve) All have very different, but known energy spectra. Cross sections known. Densities not well known, so keep absolute normalization free for each process. Fit shape of various contributions with free normalization, but normalization limited by experimental overall normalization error, which is 15% for EGRET data. Point-to-point errors  7% (yields good 2).

  9. Observed Profile z Rotation Curve x y 1/r2 halo totalDM disk 2003, Ibata et al, Yanny et al. bulge Inner Ring Outer Ring Executive Summary for fits in 360 sky directions Expected Profile xy v2M/r=cons. and M/r3 1/r2 for const. rotation curve Divergent for r=0? NFW1/r Isotherm const. xz Halo profile

  10. Excess of Diffuse Gamma Rays above 1 GeV (first publications by Hunter et al, Sreekumar et al. (1997) B C A 2004 Inv. Compton 0 Bremsstrahlung Strong, Moskalenko, Reimer, APJ.613, astro-ph/0406254 D E F A: inner Galaxy (l=±300, |b|<50) B: Galactic plane avoiding A C: Outer Galaxy D: low latitude (10-200) E: intermediate lat. (20-600) F: Galactic poles (60-900)

  11. Excess of Diffuse Gamma Rays has same spectrum in all directions compatible with WIMP mass of 50-100 GeV Egret Excess above extrapolated background from data below 0.5 GeV Statistical errors only Excess same shape in all regions implying same source everywhere Important: if experiment measures gamma rays down to 0.1 GeV, then normalizations of DM annihilation and background can both be left free, so one is not sensitive to abso- lute background estimates, BUT ONLY TO THE SHAPE, which is much better known.

  12. Diffuse Gamma Rays for different sky regions Good Fits for WIMP masses between 50 and 100 GeV A: inner Galaxy B: outer disc C: outer Galaxy E: intermediate lat. F: galactic poles D: low latitude 3 components: galactic background + extragalactic bg + DM annihilation fitted simultaneously with same WIMP mass and DM normalization in all directions. Boost factor around 70 in all directions and statistical significance > 10 !

  13. Optimized Model from Strong et al. astro-ph/0406254 Change spectral shape of electrons AND protons

  14. Optimized Model from Strong et al. astro-ph/0406254 Change spectral shape of electrons AND protons Protons Electrons Nucleon and electron spectra tuned to fit gamma ray data. Apart from the difficulty to have inhomogeneous nuclei spectra (SMALL energy losses!) the model does NOT describe the spectrum IN ALL DIRECTIONS! B/C

  15. Optimized Model from Strong et al. astro-ph/0406254 Change spectral shape of electrons AND protons 300 MeV 150 MeV 100 MeV 500 MeV 1000 MeV 2000 MeV

  16. Probability of optimized model if 2 measured in 360 sky directions and integrate data with E>0.5 GeV: 2= 962.3/324 for Optimized Model without DM +correl. errors: Prob = < 10-10 2= 306.5/323 for Optimized Model +DM +correl. errors: Prob = 0.736 Boostfactor=25 for OM vs 70 for CM Optimized Model from Strong et al. astro-ph/0406254 Change spectral shape of electrons AND protons

  17. Determining halo profile DM Gamma Ray Flux: =2  1/r2 2 Gaussian ovals

  18. H H2 4 R [kpc] Fit results of halo parameters Enhancement of rings over 1/r2 profile 2 and 7, respectively. Mass in rings 1.6 and 0.3% of total DM (<v> from WMAP) Parameter values: 14 kpc coincides with ring of stars at 14-18 kpc due to infall of dwarf galaxy (Yanny, Ibata, …..) 4 kpc coincides with ring of neutral hydrogen molecules! Boostfactor  20-200 Dokuchaev et al: 10<B<200, IDM2004

  19. Halo density on scale of 300 kpc Sideview Topview Cored isothermal profile with scale 4 kpc Total mass: 3.1012 solar masses

  20. Halo density on scale of 30 kpc Sideview Topview

  21. WITH 2 rings WITHOUT rings 100<b<200 DISC 100<b<200 DISC 200<b<900 200<b<900 50<b<100 50<b<100 Longitude fits for 1/r2 profile with/w.o. rings E > 0.5 GeV Halo parameters from fit to 180 sky directions: 4 long. profiles for latitudes <50, 50<b<100, 100<b<200, 200<b<900 (=4x45=180 directions)

  22. Longitude on linear scale ABOVE 0.5 GeV BELOW 0.5 GeV

  23. Do other galaxies have bumps in rotation curves? Sofue & Honma

  24. From Eric Hayashi

  25. Normalization of background: Compare with GALPROP, which gives absolute prediction of background from gas distributions etc.

  26. Background scaling factors Background scaling factor = Data between 0.1 and 0.5 GeV/GALPROP GALPROP = computer code simulating our galaxy (Moskalenko, Strong)

  27. Normalization of DMA -> “Boost factor” (= enhancement of DMA by clustering of DM)

  28. Clustering of DM -> boosts annih. rate Annihilation DM density squared! Clustersize: 1014 cm =10x solar system Mmin 10-8 -10-6 Mסּ Cluster density  25 pc-3 Halo mass fraction in clumps: 0.002 From Berezinsky, Dokuchaev, Eroshenko Boost factor  <2>/<>2  20-200 Clumps with Mmin give the dominant contribution to DM annihilation -> many in a given direction -> similar boost factor in all directions

  29. What about Supersymmetry? Assume mSUGRA 5 parameters: m0, m1/2, tanb, A, sign μ

  30. t t t t bb bb Annihilation cross sectionsin m0-m1/2 plane (μ > 0, A0=0) tan=5 tan=50 10-24 10-27 EGRET WMAP   WW WW For WMAP x-section of <v>2.10-26 cm3/s one needs large tanβ

  31. Coannihilations vs selfannihilation of DM If it happens that other SUSY particles are around at the freeze-out time, they may coannihilate with DM. E.g. Stau + Neutralino -> tau Chargino + Neutralino -> W However, this requires extreme fine tuning of masses, since number density drops exponentially with mass. But more serious: coannihilaition will cause excessive boostfactors Since  anni = coanni + selfanni must yield <v>=1026 cm3/s. This means if coannihilation dominates, selfannihilation  0 In present universe only selfannihilation can happen, since only lightest neutralino stable, other SUSY particles decayed, so no coannihilation. If selfannihilation x-section 0, no indirect detection. CONCLUSION: EGRET data excludes largely coannih.

  32. Stau coannihilation mA resonance WMAP EGRET EGRET excess interpreted as DM consistent with WMAP, Supergravity and electroweak constraints MSUGRA can fulfill all constraints from WMAP, LEP, b->s, g-2 and EGRET simultaneously, if DM is neutralino with mass in range 50-100 GeV and squarks and sleptons are O(1 TeV) Stau LSP Incomp. with EGRET data No EWSB Bulk

  33. SUSY Mass spectra in mSUGRA compatible with WMAP AND EGRET Charginos, neutralinos and gluinos light LSP largely Bino  DM is supersymmetric partner of CMB

  34. Unification of gauge couplings SM SUSY Update from Amaldi, dB, Fürstenau, PLB 260 1991 With SUSY spectrum from EGRET data and start values of couplings from final LEP data perfect gauge coupling unification possible

  35. DAMA ZEPLIN Edelweiss CDMS Projections Comparison with direct DM Searches Spin-dependent Spin-independent Predictions from EGRET data assuming Supersymmetry

  36. Positron fraction and antiprotons from present balloon exp. Signal Signal Background Background Positrons Positrons Antiprotons Antiprotons SAME Halo and WIMP parameters as for GAMMA RAYS but fluxes dependent on propagation! DMA can be used to tune models: at present no convection, nor anisotropic diffusion in spiral arms.

  37. Summary EGRET excess shows all key features from DM annihilation: Excess has same shape in all sky directions: everywhere it is perfectly (only?) explainable with superposition of background AND mono-energetic quarks of 50-100 GeV Results and x-sect. in agreement with SUPERSYMMETRY Excess follows expectations from galaxy formation: 1/r2 profile with substructure, visible matter/DM0.02 Excess connected to MASS, since it can explain peculiar shape of rotation curve These combined features provide FIRST (>10) EVIDENCE that DM is not so dark and follow ALL DMA expectations imagined so far. Conventional models CANNOT explain above points SIMULTANEOUSLY, especially spectrum of gamma rays in all directions, DM density profile, shape of rotation curve, stability of ring of stars at 14 kpc,..

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