Speaker
Description
The ability of direct detection experiments to constrain dark matter properties depends sensitively on the phase-space distribution of dark matter near the Sun, which can be modeled theoretically with hydrodynamical simulations of Milky Way–like galaxies. In this work, we use a sample of nearly one hundred such galaxies from the TNG50 simulation to characterize the expected phase-space distribution of dark matter. In over 90% of halos, the dark matter at the Solar position co-rotates with the baryonic disk, with median azimuthal velocities of 12–39 km/s (16th–84th percentile). This reduces the expected geocentric dark matter flux by ~5% relative to the prediction from the Standard Halo Model, and the flux occupies a ~10% larger region on the sky. As a result, the rate of isotropic nuclear scattering in a fiducial Xenon-based detector can be diminished by up to 40% near threshold, and the expected reach of a directional detector is reduced by as much as 60% at peak sensitivity. The severity of this suppression is strongly correlated with the azimuthal velocity, and a determination of this quantity to within 20 km/s from studies of the Milky Way's formation history would reduce the velocity distribution–induced astrophysical uncertainty on the dark matter–nucleon scattering rate to as low as 5%.