1. The Dark Matter Problem astrophysical probe of particle nature of DM 毕效军 中国科学院高能物理所 2009/12/16

2. Outline What we have learned from astrophysics evidence of DM and its abundance DM is not baryonic DM is not hot “ problems ” of LCDM model cuspy halos and missing satellites alternative models of DM astrophysical answers What we learned from particle physics WIMP: the classic CDM direct detection indirect detection: excesses of electrons and positrons non-standard CDM

3. 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)

4. dynamics of galaxy cluster Virial theorem U=2K K =  m i v i 2 U ~ GM 2 /R mass to light ratio (B) typical cluster: 100/h-300/h  Sun stellar pop: 1-10  Sun critical: 1390 h +- 35% Coma cluster

5. X-ray cluster hydrostatic equilibrium beta model: However, X-ray emission measures the temperature and M/Mvisible=20

6. Strong Gravitational Lensing

7. Weak Lensing mass reconstruction RXJ1347.5-1145 (Bradac et al 2005) Image ellipticity -> shear-> invert the equation

8. Cosmological scale the WMAP result Spergel et al 2003  m h 2 =0.135+-0.009  m =0.27+-0.04 WMAP Combined fit: Results depend on Supernovae and Hubble constant data.

9. Non-baryonic From BBN and CMB, it has  B h 2 =0.02+-0.002. Therefore, most dark matter should be non- baryonic.  DM h 2 =0.113+-0.009

10. Nature of the dark matter — Hot or cold Hot dark matter is relativistic at the collapse epoch and free-streaming out the galaxy-sized over density. Larger structure forms early and fragments to smaller ones. Cold DM is non-relativistic at de-coupling, forms structure in a hierarchical, bottom-up scenario. HDM is tightly bound from observation and LSS forma- tion theory

11. What we learned In the universe there exists non- baryonic, non-hot, dark matter

12. Problems at small scale of CDM Galactic satellite problem and cusp at GC Nature of dark matter or astrophysics process?

13. Predicted number Observed number of luminous satellite galaxies The predicted number of substructures exceeds the luminous satellite galaxies: dark substructures? Satellite galaxies are seen in Milky Way, e.g. Saggittarius, MCs 20km/s100km/s10km/s

14. The first dark halos Due to collisional damping and free-streaming, the smallest halo (no sub-structure) is 10 -6 solar mass (earth mass) for neutralino. Detection of such halo may probe the nature of DM. Diemand, Moore, Stadel 2005

15. Universal Density Profile NFW profile Navarro, Frenk, White 1997 Cusp Dark matter distribution—Density profile Observation of rotation curve favors cored profile strongly

16. Dark matter halo profile simulation (Navarro, Frenk, white 1996): cusp observation: core NFW96, rotation curve

17. Nature of dark matter or astrophysics process?

18. missing satellites: CDM solution satellites do exist, but star formation suppressed (after reionization?) satellites orbit do not bring them to close interaction with disk, so they will not heat up the disk. Local Group dwarf velocity dispersion underestimated halo substructure may be probed by lensing (still controversial) galaxy may not follow dwarf

19. Alternatives to CDM WDM: reduce the small scale power Self-Interacting Dark Matter (Spergel & Steinhardt 2000) Strongly Interacting Massive Particle Annihilating DM Decaying DM Fuzzy DM

20. WDM From Jing 2000

21. SIDM DM strongly interact with itself, but no EM interaction can create an core in hierachical scenario (eventually core collapse -> isothermal profile) Interaction strength: comparable to neutron-neutron Difficulty: make spherical clusters: against lensing

22. SIMP Motivation: SIDM may have QCD interaction but not EM Not detectable in WIMP search, blocked. CMB & LSS constraint: Before decoupling, photons and baryons are tightly coupled, interaction with baryon will cause additional damping of perturbation

23. From particle physics

24. Thermal history of the WIMP (thermal production) At T >> m, At T < m, At T ~ m/22, ， decoupled, relic density is inversely proportional to the interaction strength For the weak scale interaction and mass scale (non-relativistic dark matter particles), if and WIMP is a natural dark matter candidate giving correct relic density (proposed trying to solve hierarchy problem). Thermal equilibrium abundance

25. Collisional Damping and Free Streaming Initial density perturbation is damped by the free streaming of the particles before radiation-matter equality perturbations on scales smaller than r FS is smoothed out. Kinetic decoupling at T ~ 1 MeV (Chen, Kamionkowski, Zhang 2001) This is why we introduce hot, warm, and cold dark matter.

26. Detection of WIMP Indirect detection DM increases in Galaxies, annihilation restarts( ∝ ρ 2 ); ID looks for the annihilation products of WIMPs, such as the neutrinos, gamma rays, positrons at the ground/space-based experiments Direct detection of WIMP at terrestrial detectors via scattering of WIMP of the detector material.   Direct detection  p e+e+  _ indirect detection

28. Summary of the present limits

30. PAMELA results of antiparticles in cosmic rays Nature 458, 607 (2009) Positron fraction Antiproton fraction Phys.Rev.Lett.102:051101,2009 400+ citations after submitted on 28th Oct. 2008, 1paper per day

31. The total electron+positron spectrum Chang et al. Nature456, 362 2008 ATIC bumpFermi excess Phys.Rev.Lett.102:181101,2009

32. 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.

33. J. Zavala, M. Vogelsberger, and S. White, Astro- ph/0910.5221 Astro-ph/0911.0422

34. Breit-Wigner enhancement and fine tunning We require delta, gamma ~ 10 -4 to boost ~1000. Bi, He, Yuan, Astro-ph/0903.0122 Ibe, Murayama, Yanagida Guo, Wu

35. Emission from the GC Constraint on the central density of DM Tension Exist for the annihilating DM scenario, but consistent with decay scenario Bi et al., 0905.1253 Liu, Yuan, Bi, Li, Zhang, 0906.3858

36. Constraints on the minimal subhalos by observations of clusters Standard CDM predicts the minimal subhalos Observation constrains Fermi limit to DM is warm A. Pinzke et al., 0905.1948

37. Nonthermal production of dark matter 暗物质可以通过早期宇宙 产物的衰变产生，这样的 暗物质可以有很大的湮灭 截面，同时产生的速度大， 压低小尺度的结构。这样 银心的伽马射线没有超出， 因此受到的限制会减弱。 银心的伽马射线、河外星 系团、河外弥散伽马的限 制可以满足 Lin, Huang, Zhang, Brandenberger, PRL86,954 (2001) Bi, Brandenberger, Gondolo, Li, Yuan, Zhang, 0905.1253