September 19, 20132:00 pm – 3:00 pm (CDT)

## Dark Matter in the Galaxy: Rotation Curve and the Phase Space Distribution of Milky Way’s Dark Matter Particles

Speaker:

Pijush Bhattacharjee (SINP & Washington University)

Location:

A large number of experiments worldwide are currently trying to directly detect the hypothetical Weakly Interacting Massive Particles (WIMPs) thought to constitute the Dark Matter (DM) halo of our Galaxy, by looking for nuclear recoil events due to scattering of WIMPs off nuclei of suitably chosen detector materials in low background underground facilities. The rate of nuclear recoil events depends on the local (i.e., solar neighborhood) density and velocity distribution of the WIMPs in the Galaxy. These are a priori unknown. Estimates based on a variety of observational data typically yield values for the local density of DM in the range 0.2 -- 0.4 GeV/cm^3. In contrast, not much knowledge directly based on observational data is available on the likely form of the velocity distribution function (VDF) of the WIMPs in the Galaxy. The standard practice is to use what is often referred to as the Standard Halo Model” (SHM), in which the DM halo of the Galaxy is described as a single-component isothermal sphere, for which the VDF is assumed to be isotropic and of Maxwell-Boltzmann form, with a velocity dispersion of about 270 km/s and a truncation at an assumed value of the local escape speed. Apart from several theoretical issues concerning the self-(in) consistency of the SHM as a model of a finite-size, finite-mass DM halo of the Galaxy, recent high resolution cosmological simulations of DM halos give strong indications of significant departure of the VDF from the Maxwellian form. In this talk we discuss how we can derive the VDF of the DM particles in the Galaxy directly from the observational rotation curve data for the Galaxy. We also discuss the implications for the interpretation of the results of DM direct detection experiments.