Dark matter annihilation and detection

1. Dark matter annihilation and detection X.J. Bi (IHEP) 2006.8.28

2. Outline • Annihilation signals from the subhalos and the detection. • GeV excess of diffuse gamma by EGRET and its possible explanation. • Positron excess of HEAT and its possible explanation. • An interesting dark matter model which predicts a heavy charged stable particle.

3. Subhalos in the MW halo Moore et al • The DM annihilation flux is proportional to the DM density square • A wealth of subhalos exist due to high resolution simulations.

4. The first generation object Diemand, Moore & Stadel, 2005: • Depending on the nature of the dark matter: for neutralino-like dark matter, the first structures are mini-halos of 10-6M⊙. • There would be zillions of them surviving and making up a sizeable fraction of the dark matter halo. • The dark matter detection schemes may be quite different!

5. g-rays from the subhalos Reed et al, MNRAS357,82(2004) g-rays from subhalos source y g-rays from smooth bkg sun GC

6. Statistical results • The curves are due to different author’s simulations. • The threshold is taken as 100 GeV. • The susy factor is taken an optimistic value for neutralino mass between 500 GeV and 1TeV. • Results are within the field of view of ARGO.

7. Instruments with large field of view and their sensitivities • GLAST • ARGO/HAWC

8. Gamma ray detection from DM annihilation Complementary capabilities ground-based space-based ACTEASPair angular resolution good fair good duty cycle low high high area large large small field of view small large large+ can reorient energy resolution good fair good, with smaller systematic uncertainties HAWC~0.04ICRAB my estimate

9. Sensitivity at ARGO（95％C.L.）

10. 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.

11. 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.

12. Hard proton or electron injection index

13. Contribution from DM

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

15. With and without subhalos

16. 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

17. Results of different regions

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

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

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

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

22. 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.

23. 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:

24. 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

25. 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

26. 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.

27. 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.

28. 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

29. 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.