Dark matter annihilation and the Milky Way diffuse gamma

1. Dark matter annihilation and the Milky Way diffuse gamma X.J. Bi (IHEP) 2006.8.28

2. Outline • Introduction to dark matter annihilation. • GeV excess of diffuse gamma by EGRET and its possible explanation. • Positron excess of HEAT and its possible explanation.

3. Cosmology/astrophysics/particle physics

4. From de Boer

5. Evidences — cluster scale • Cluster contains hot gas which is at hydro static equilibrium. It’s temperature follows, • However, X-ray emission measures the temperature and M/Mvisible=20

6. Evidences — cluster scale • Weak lensing measures the distortion of images of background galaxies by the foreground cluster, which measures the cluster mass. • Sunyaev-Zeldovich distortion measures the distortion of CMB passing through cluster, which measure the temperature of the gas and therefore the mass of the cluster. • …other measurements

7. Evidences — galaxy scale • From the Kepler’s law, for r much larger than the luminous terms, you should have v∝r-1/2 However, it is flat or rises slightly. • The most direct evidence of the existence of dark matter. Corbelli & Salucci (2000); Bergstrom (2000)

8. Evidences — cosmological scale • WMAP measures the anisotropy of CMB, which includes all relevant cosmological information. A global fit combined with other measurements gives (SN, LSS…) the cosmological paramters precisely. mh2=0.135+-0.009 m=0.27+-0.04 Spergel et al 2003

9. Non-baryonic DM From BBN and CMB, it has Bh2=0.02+-0.002. Therefore, most dark matter should be non-baryonic. DMh2=0.113+-0.009 Non-baryonic dark matter dominates the matter contents of the of the Universe.

10. Energy budget of the universe

11. Problems related with dark matter • What particle form dark matter? • Is there one or many spices of dark matter particles? • What are the dark matter’s quantum numbers? • How and when was it produced? • How to explain the observed value of ? • How is dark matter distributed? • The role in structure formation; How does structure form? • The two sides are closely related: The nature certainly affect the structure formation, ex. hot, cold and warm are different, interacting, decaying dark matter have implications in structure formation. • The evidences come from gravitational effects, which however shed no light on the nature of DM. On the study of effects other than gravity, we will show latter that particle physics and astrophysics/cosmology are closely related.

12. cosmology CMB, LSS, lensing … Astrophysics, high energy gamma, neutrino Particle physics Dark matter Collider physics

13. Constrains on the SUSY parameter space • The blue stripe is allowed by WMAP J. Ellis et al (2004)

14. Gamma rays • Monoenergetic line • Continuous spectrum A smoking gun of DM ann. The flux is suppressed due to loop production. Larger flux. Need careful analysis of the background

15. Neutrinos from the sun or the earth • Density at the solar center is determined by the scattering, insensitive to the local density • The present data gives constraints on the parameter space • IceCube can cover most paramter space

17. Diffuse gamma rays of the MW • COS-B and EGRET (20keV~30GeV) observed diffuse gamma rays, measured its spectra. • Diffuse emission comes from nucleon-gas interaction, electron inverse Compton and bremsstrahlung. Different process dominant different parts of spectrum, therefore the large scale nucleon, electron components can be revealed by diffuse gamma.

18. GeV excess of spectrum • Based on local spectrum gives consistent gamma in 30 MeV~500 MeV, outside there is excess. • Harder proton spectrum explain diffuse gamma, however inconsistent with antiproton and position measurements.

19. Hard proton or electron injection index

20. Contribution from DM

21. Fit the spectrum Enhancement by substructures • B~100 • Fi,j ----- Adjust the propagation parameters

22. The SUSY factor The integrated flux due to different threshold energy. Points are different SUSY model

23. With and without subhalos

24. Calculate cosmic rays • Adjust the propagation parameter to satisfy all the observation data and at the same time satisfy the egret data after adding the dark matter contribution

25. Results of different regions

26. HEAT and positron excess • HEAT found a positron excess at ~10 GeV B~100-1000

27. Enhancement by subhalos • The average density (for annihilation) is improved with subhalos. • The corresponding positron flux is improved.

28. Result • The positron fraction can be explained still need a boost factor of about 2~3

29. Uncertainties in positron flux • Large uncertainties from propagation • Uncertainties by the realization of the subhalos distribution.

30. Conclusion • In any new physics beyond SM predicting new stable particle predicts the DM in the universe and the existence of DM is confirmed by astrophysics observations. • Taking the contribution from DM annihilation into account the EGRET data can be explained perfectly. (Without DM it is difficult to explain the GeV excess even there are large uncertainties of cosmic ray propagation). • Positron excess in HEAT can also be explained by adding contribution from DM annihilation. • Both the EGRET data and HEAT require DM subhalos with very cuspy profile.

31. Unified model of dark matter and dark energy • Possible candidates of dark energy are the cosmological constant or a scalar field --- the quintessence field (a dynamical fundamental scalar field). • The motivation is to build a unified model of dark matter and dark energy in the framework of supersymmetry. • requiring a shift symmetry of the system, the quintessence is always kept light and the potential is not changed by quantum effects. If is the LSP, it is stable and forms DM.

32. Shift symmetry and interaction • To keep the shift symmetry the quintesssence field can only coupled with matter field derivatively. We consider the following interactions and derive their supersymmetric form:

33. 106 Non-thermal production of quintessino WIMP  quintessino + SM particles (WIMP=weakly interacting massive paricle) SM quintessino WIMP Since the interaction of quintessino is usually suppressed by Planck scale, it is generally called superWIMP. e.g. Gravitino LSP quintessino LKK graviton

34. Charged slepton, sneutrino Or neutralino/chargino EM, had. cascade  change CMB spectrum  change light element abundance predicted by BBN Candidates of NLSP WIMP  quintessino + SM particles 105 s  t  107 s OK Charged slepton NLSP are allowed by the model

35. Effects of the model • Suppress the matter power spectrum at small scale (flat core and less galaxy satellites). • Faraday rotation induced by quintessence. • Suppress the abundance of 7Li. • The lightest super partner of SM particles is stau.

36. Look for heavy charged particles • A charged scalar particle with life time of 105 s  t  107 s and mass 100 GeV< M < TeVis predicted in the model. • High energy comic neutrinos hit the earth and the heavy particles are produced and detected at L3C/IceCube • Due to the R-parity conservation, always two charged particles are produced simultaneously and leave two parallel tracks at the detector.

37. Production at colliders • If is the LSP of SM, all SUSY particles will finally decay into and leave a track in the detector. • Collecting these , we can study its decay process. (We can even study gravity at collider.) • LHC/ILC can at most produce Buchmuller et al 2004 Kuno et al., 2004 Feng et al., 2004

38. Conclusion • In the CDM scenario, LSS form hierarchically. The MW is distributed with subhalos. • Taking the contribution from DM annihilation into account the EGRET data can be explained perfectly. (Without DM it is difficult to explain the GeV excess even there are large uncertainties of cosmic ray propagation). • Positron excess in HEAT can also be explained by adding contribution from DM annihilation. • Both the EGRET data and HEAT require DM subhalos with very cuspy profile. • A DM-DE unified model requires stau being the NLSP (gravitino model). Make different phenomenology.