Gamma-ray emission from warm WIMP annihilation Qiang Yuan Institute of High Energy Physics Collaborated with Xiaojun Bi, Yixian Cao, Jie Liu, Liang Gao, Pengfei Yin & Xinmin Zhang (arXiv:1203.5636) TPCSF cosmology workshop 2012-05-23

Outline Introduction of cold/warm dark matter Gamma-ray emission of warm WIMP based on numerical simulations Conclusion

Structure evolution: cold dark matter Bottom-up structure formation pattern instead of top-down pattern (fragmentation): cold dark matter Springel et al. (2006) Nature CDM simulation vs. galaxy survey

How cold is dark matter? The coldness of dark matter depends on the free-streaming scale during the formation of structures Hot dark matter (eV neutrinos) that washes out fluctuations on cluster scale (10 Mpc/h) Warm dark matter (sterile neutrinos) that washes out fluctuations on galaxy scale (1 Mpc/h) Cold dark matter that has effectively zero thermal velocity From Jing’s Nanjing talk (2012)

How cold is dark matter: matter power spectrum WDM CDM Tegmark et al. (2004)

How cold is dark matter: number of satellites Jing (2001)

How cold is dark matter: circular velocity of Milky Way satellites Lovell et al. (2012)

How cold is dark matter: velocity width function of galaxies (ALFALFA survey) Papastergis et al. (2011)

How cold is dark matter: central density of dwarf galaxies Burkert (1995) From Shi Shao (2012)

Observational summary Large scale structures are very close to CDM At (sub-)galactic scales, many discrepancies between observations and CDM expected (abundance, density profile, velocity profile) WDM can better explain the observations

If it is conventional WDM (like sterile neutrino), it is fatal for DM detection However, the non-thermal production can make WIMPs warm (Jeannerot et al. 1999; Lin et al. 2001; Bi et al. 2009)

Outline Introduction of cold/warm dark matter Gamma-ray emission of warm WIMP based on numerical simulations Conclusion

Simulations NT-WDM 1 keV WDM Lin et al. (2001) Lovell et al. (2012)

Subhalo statistics M vs. L≡∫2dV M vs. F≡L/d2

Spatial skymaps: CDM

Spatial skymaps: WDM

Two supersymmetric benchmark models Total skymaps with diffuse background (E>10 GeV)

Detectability comparison

Conclusion Subhalos are less abundant for WDM, resulting a very flat subhalo luminosity function It is currently difficult to detect either the cold or warm WIMPs, but the detectability of warm WIMP can be in principle better than cold WIMP due to a potentially larger cross section For DM indirect search strategy, the Galactic center may be prior to dwarf galaxies for warm WIMP scenario (different from that for cold WIMPs)

Thank you