Mitchell Institute for Fundamental Physics & Astronomy
College Station, Texas 77843
The spatial and velocity distributions of dark matter in the Milky Way Halo affect the signals expected to be observed in searches for dark matter. Results from direct detection experiments are often analyzed assuming a simple isothermal distribution of dark matter, the Standard Halo Model (SHM). Yet there has been skepticism regarding the validity of this simple model due to the complicated gravitational collapse and merger history of actual galaxies. We compare the SHM to the results of detailed simulations of structure formation to investigate whether or not the SHM is a good representation of the true WIMP distribution in the analysis of direct detection data. We examine two Milky Way-like galaxies from the MaGICC simulations of galaxy formation, obtained in cosmological simulations with (a) dark matter only and (b) with baryonic physics included. The inclusion of baryons drives the shape of the DM halo to become more spherical and makes the velocity distribution of dark matter particles more isotropic, thereby making the SHM a better fit. We conclude that in the Solar neighborhood, the SHM is in fact a good approximation to the true dark matter distribution for the purpose of dark matter direct detection calculations.