Reverse Direct Detection: Cosmic Ray Scattering With Light Dark Matter

TL;DR

This paper introduces a novel 'reverse direct detection' method where cosmic ray propagation is used to detect light dark matter through its elastic scattering with particles in space, setting new constraints on dark matter interactions.

Contribution

It proposes a new cosmic-ray based approach to constrain light dark matter interactions, providing competitive and improved limits over existing methods.

Findings

Set new limits on dark matter-proton cross sections, competitive with cosmological constraints.

Established improved bounds on dark matter-electron interactions for certain mass ranges.

Demonstrated the potential of cosmic ray observations to probe light dark matter properties.

Abstract

Sub-GeV dark matter candidates are of increasing interest, because long-favored candidates such as GeV-scale WIMPs have not been detected. For low-mass dark matter, model-independent constraints are weak or nonexistent. We show that for such candidates, because the number density is high, cosmic ray propagation can be affected by elastic scattering with dark matter. We call this type of search `reverse direct detection,' because dark matter is the target and Standard Model particles are the beam. Using a simple propagation model for galactic cosmic rays, we calculate how dark matter affects cosmic ray spectra at Earth, and set new limits on the dark matter-proton and dark matter-electron cross sections. For protons, our limit is competitive with cosmological constraints, but is independent. For electrons, our limit covers masses not yet probed, and improves on cosmological constraints by one to two orders of magnitude. We comment on how future work can significantly improve the sensitivity of cosmic-ray probes of dark matter interactions.