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The Dark Matter Problem astrophysical probe of particle nature of DM

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. 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

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The Dark Matter Problem astrophysical probe of particle nature of DM

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  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 =  mi vi2 U ~ GM2/R Coma cluster mass to light ratio (B) typical cluster: 100/h-300/h Sun stellar pop: 1-10 Sun critical: 1390 h +- 35%

  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 Image ellipticity -> shear-> invert the equation RXJ1347.5-1145 (Bradac et al 2005)

  8. Cosmological scalethe WMAP result Spergel et al 2003 WMAP Combined fit: mh2=0.135+-0.009 m=0.27+-0.04 Results depend on Supernovae and Hubble constant data.

  9. Non-baryonic From BBN and CMB, it has Bh2=0.02+-0.002. Therefore, most dark matter should be non-baryonic. DMh2=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. Satellite galaxies are seen in Milky Way, e.g. Saggittarius, MCs Predicted number Observed number of luminous satellite galaxies 10km/s 20km/s 100km/s • The predicted number of substructures exceeds the luminous satellite galaxies: dark substructures?

  14. The first dark halos Diemand, Moore, Stadel 2005 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.

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

  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) Thermal equilibrium abundance 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).

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

  26. c c _ g p c c e+ n Detection of WIMP • Indirect detection DM increases in Galaxies, annihilation restarts(∝ρ2); 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. indirect detection Direct detection

  27. Summary of the present limits

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

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

  30. 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.

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

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

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

  34. 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

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