1. Can dark matter annihilation account for the cosmic e+- excesses?
Bi Xiao-Jun
IHEP, CAS
Dark matter, dark energy, matter-antimatter asymmetry, Tsinghua University, Taiwan

2. PAMELA results of antiparticles in cosmic rays
Positron fraction
Antiproton fraction
PAMELA released data on the positron/electron ratio up to about 100 GeV, which show clear excess above ~10 GeV. The low energy data is affected by the solar environment and we do not need care it too much.
Nature 458, 607 (2009)
Phys.Rev.Lett.102:051101,2009
390 citations after submitted on 28th Oct. 2008, 1paper per day

3. The total electron+positron spectrum
ATIC bump
Fermi excess
Chang et al. Nature456,
Phys.Rev.Lett.102:181101,2009

4. Possible explanations
Astrophysical sources
Exotic sources
Nearby SNRs, pulsars
Propagation
Early SN stage interaction of CRs
Dark matter annihilation
Dark matter decay

5. Possible origins of e+e-: pp interaction (Blasi, 0903.2794)
Occur at the cosmic ray acceleration source: hard spectrum
If we consider some new processes, we may first consider within cosmic rays physics
Comment: nature for Fermi spectrum;
antiprotons may set constraints on this picture

6. From CRs interaction There is knee in CR spectrum at ~10^15 eV
(Hu, Bi et al., )
There is knee in CR spectrum at ~10^15 eV
It is proposed the knee is generated by interaction, with Eγ=1eV, the threshold energy is at ~10^15 eV
3% converted can explain the ATIC or Fermi Fermi excess
Pamela is related with knee; the knee is at knee; knee is generated by the pair production. It should be noted that for 1ev the threshold energy is just at the knee. By simulation

7. Nearby pulsars

8. Astrophysical sources
D. Hooper et al.
S. Profumo ……
Nearby pulsars:

10. Many possible astrophysical solutions to explain the excesses are proposed. However, these sources are easy to account for the Fermi spectrum, not easy for ATIC.

11. Possible explanations
Astrophysical sources
Exotic sources
Nearby SNRs, pulsars
Propagation
Early stage interaction of CRs
Dark matter annihilation
Dark matter decay
ATIC ??
Fermi
ATIC OK

12. Primary positron/electrons from dark matter – implication from new data
DM annihilation/decay produce leptons mainly in order not to produce too much antiprotons.
Very hard electron spectrum -> dark matter annihilates/decay into leptons.
Very large annihilation cross section, much larger (~1000) than the requirement by relic density.
1) nonthermal production,
2) Sommerfeld enhancement
3) Breit-Wigner enhancement
4) dark matter decay.

13. positron ratio from DM annihilation
Yin, et al. arXiv:

14. Global fit to the ATIC or Fermi and PAMELA data
Liu, Yuan, Bi, Li, Zhang,
Astro-ph/

15. Possible explanations
Astrophysical sources
Exotic sources
Nearby SNRs, pulsars
Propagation
Early stage interaction of CRs
Dark matter annihilation
Dark matter decay
ATIC ??
Fermi
ATIC OK OK OK

16. How to have so large flux
Very large annihilation cross section, much larger (~1000) than the requirement by relic density.
1) nonthermal production, ,suppress gamma
2) Sommerfeld enhancement
3) Breit-Wigner enhancement
4) dark matter decay.

17. Sommerfeld enhancement
Kinematically suppression
Mass of φis about 1GeV, is
Kinematically suppressed to antiprotons;
At the same time attractive interaction can enhance the annihilation rate, Sommerfeld enhancement. (Arkani-Hamed et al   )
For Coulomb potential we have
To enhance the dark matter annihilation we have long range attractive force

18. Fine tunning of Sommerfeld enhancement
Yuan, Bi, Liu, Yin, Zhang and Zhu, Astro-ph/

19. J. Zavala, M. Vogelsberger, and S. White, Astro-ph/0910.5221

20. Breit-Wigner enhancement and fine tunning
Bi, He, Yuan,
Astro-ph/
We require delta, gamma ~ 10-4 to boost ~1000.

21. Constraints on the dark matter annihilation scenario
Since the DM annihilation rate is very large, they imply the existence of an abundant population of e+- in the galactic halo, dwarf galaxies, galaxy clusters, galactic center, or at the early Universe. The abundance of e+- may induce observables that can be constrained by the present experiments.

22. Constraints from CMB
DM annihilation heats and ionizes the photon-baryon plasma at z~1000, constrained by WMAP and Planck
T.R. Slatyer et al.,

23. Constraints on the minimal subhalos by observations of clusters
A. Pinzke et al.,
Standard CDM predicts the minimal subhalos
Observation constrains
Fermi limit to
DM is warm

24. Constraints from extragalactic diffuse gamma rays
S. Profumo et al.,

25. Constraint by Galactic diffuse gamma rays
M. Cirelli et al.,

26. Emission from the GC Constraint on the central density of DM Tension
Bi et al.,
Constraint on the central density of DM
Tension
Exist for the
annihilating
DM scenario,
but consistent
with decay scenario
annihilation
decay
Liu, Yuan, Bi, Li, Zhang,

27. Constraints from the diffuse gamma ray emission
Zhang, Yuan, Bi,

28. Possible explanations
Astrophysical sources
Exotic sources
Nearby SNRs, pulsars
Propagation
Early stage interaction of CRs
Dark matter annihilation ?
Dark matter decay
ATIC ??
Fermi
ATIC OK OK OK

29. Summary ATIC DM Fermi Annihilation: how to boost? Strong constraints!
Decay: how to get such long life time, ~1026s
Astrophysical sources: difficult to test;
(century problems: origin of CRs, knee of CRs