Boosted Dark Matter from Cosmic-Ray Collisions: Fluxes, Recoil Energies and Rates in Large Underground Detectors

This study computes the flux of dark matter particles boosted to relativistic or semi-relativistic speeds by collisions with cosmic rays, and the recoil signals such particles would produce in large underground detectors. Boosting solves the threshold problem for light candidates: a MeV-scale particle that would leave an undetectable recoil at halo speeds can leave a kiloelectronvolt recoil after a cosmic-ray collision. The price is flux, which falls with the same scattering cross section that produces the detectable recoil, so the signal scales as the square of the cross section and the reachable region in parameter space is a band rather than a half-plane. Large neutrino detectors, not dedicated dark matter detectors, set the relevant exposures. All results are computed, not measured.