Bounds on boosted dark matter from direct detection: The role of energy-dependent cross sections

TL;DR

This paper derives bounds on boosted dark matter-electron scattering cross sections using direct detection data, emphasizing the importance of energy-dependent cross sections and comparing results across different mediator regimes.

Contribution

It introduces a method to incorporate energy-dependent cross sections in deriving dark matter bounds, improving upon previous analyses that assumed constant cross sections.

Findings

Bounds on DM-electron cross sections are significantly affected by energy dependence.

Boosted light dark matter can be constrained using existing direct detection data.

Energy-dependent analysis alters the interpretation of experimental limits.

Abstract

The recoil threshold of Direct Detection experiments limits the mass range of Dark Matter (DM) particles that can be detected, with most DD experiments being blind to sub-MeV DM particles. However, these light DM particles can be boosted to very high energies via collisions with energetic Cosmic Ray electrons. This allows Dark Matter particles to induce detectable recoil in the target of Direct Detection experiments. We derive constraints on scattering cross section of DM and electron, using XENONnT and Super-Kamiokande data. Vector and scalar mediators are considered, in the heavy and light regimes. We discuss the importance of including energy dependent cross sections (due to specific Lorentz structure of the vertex) in our analysis, and show that the bounds can be significantly different than the results obtained assuming constant energy-independent cross-section, often assumed in the literature for simplicity. Our bounds are also compared with other astrophysical and cosmological constraints.