Constraining light dark matter upscattered by ultrahigh-energy cosmic rays

TL;DR

This paper demonstrates that ultrahigh-energy cosmic rays can be used to constrain ultralight dark matter particles, with constraints being largely independent of dark matter mass for a power-law spectrum.

Contribution

It introduces a method to extend dark matter constraints to ultralight particles using ground-based UHECR measurements, independent of dark matter mass.

Findings

Constraints can reach below eV scale for ultralight DM.

Constraints are insensitive to DM mass for a power-law CR spectrum.

UHECR data can extend current limits on dark matter interactions.

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 $\mathcal{O}(10^{-31})\text{ cm}^{2}$ for a constant DM-nucleon scattering cross section. We show that if the CR energy spectrum follows a power law of type $\sim E^{-3}$, 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 $\sim10^{20}\text{ eV}$. 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.