Constraining light dark matter upscattered by ultrahigh-energy cosmic rays

Abstract

Light halo dark matter (DM) particles upscattered by high-energy cosmic rays (CRs) can be energetic, and become detectable by conventional direct detection experiments. The current constraints derived from space-based direct CR measurements can reach O(10−31) cm2 for a constant DM-nucleon scattering cross section. We show that if the CR energy spectrum follows a power law of type ∼E−3, the derived constraints on the scattering cross section will be highly insensitive to DM particle mass. This suggests that ultrahigh-energy CRs (UHECRs) indirectly measured by ground-based detectors can be used to place constraints on ultralight DM particles, as E−3 is a very good approximation of the UHECR energy spectrum up to energy ∼1020 eV. Using the recent UHECR flux data, we show that the current constraints derived from space-based CR measurements can in principle be extended to ultralight DM particles far below eV scale.