Dark matter at the end of the Galaxy

Abstract

Dark matter density profiles based upon Lambda-CDM cosmology motivate an\nansatz velocity distribution function with fewer high velocity particles than\nthe Maxwell-Boltzmann distribution or proposed variants. The high velocity tail\nof the distribution is determined by the outer slope of the dark matter halo,\nthe large radius behavior of the Galactic dark matter density. N-body\nsimulations of Galactic halos reproduce the high velocity behavior of this\nansatz. Predictions for direct detection rates are dramatically affected for\nmodels where the threshold scattering velocity is within 30% of the escape\nvelocity.\n