Asymmetric Velocity Distributions from Halo Density Profiles in the Eddington Approach

Abstract

In the present paper we show how obtain the energy distribution f (E) in our vicinity starting from WIMP density profiles in a self consistent way by employing the Eddington approach and adding reasonable angular momentum dependent terms in the expression of the energy. We then show how we can obtain the velocity dispersions and the asymmetry parameter ]beta in terms of the parameters describing the angular momentum dependence. From this expression for f (E) we proceed to construct an axially symmetric WIMP velocity distributions, which for a gravitationally bound system automatically has an velocity upper bound and is characterized by the the same asymmetries. This approach is tested and clarified by constructing analytic expressions in a simple model, with adequate structure. We then show how such velocity distributions can be used in determining the event rates, including modulation, both in the standard as well directional WIMP searches. find that some density profiles lead to approximate Maxwell-Boltzmann distributions, which are automatically defined in a finite domain, i.e. the escape velocity need not be put by hand. The role of such distributions in obtaining the direct WIMP detection rates, including the modulation, is studied in some detail and, in particular, the role of the asymmetry is explored.

Dark matter capture by the Sun: revisiting velocity distribution uncertainties

“…The formalism and uncertainties related to DM capture by the Sun are treated in [1,32], we revisit in this work the astrophysical uncertainties related to dark matter distributions such as the local DM density and velocity distribution. Different assumptions can be inferred from cosmological simulations, galactic dynamics and other approaches (see e.g [33][34][35][36][37][38]). Furthermore, DM only [39,40] or detailed hydrodynamical simulations of Milky Way size halos inhabited by a disc galaxy often show departure from the standard Maxwellian description of the DM halo velocities distribution [41][42][43][44][45][46].…”