Attenuation of Cosmic Ray Electron Boosted Dark Matter

TL;DR

This paper investigates how cosmic ray electrons can boost dark matter to relativistic energies, leading to flux attenuation at Earth, and analyzes the implications for direct detection constraints across different models.

Contribution

It provides analytical and numerical analysis of flux attenuation for boosted dark matter, demonstrating model independence for certain mass ranges, and emphasizes the need to re-evaluate detection constraints.

Findings

Attenuation ceiling varies with dark matter mass.

Flux attenuation is nearly model-independent for heavy DM and mediators.

Re-evaluating direct detection constraints with energy-dependent scattering is crucial.

Abstract

We consider a model of boosted dark matter (DM), where a fraction of DM is upscattered to relativistic energies by cosmic ray electrons. Such interactions responsible for boosting the DM also attenuate its flux at the Earth. Considering a simple model of constant interaction cross-section, we make analytical estimates of the variation of the attenuation ceiling with the DM mass and confirm it numerically. We then extend our analysis to a $Z'$-mediated leptophilic DM model. We show that the attenuation ceiling remains nearly model-independent for DM and mediator particles heavier than the electron, challenging some previous discussions on this topic. Using the XENONnT direct detection experiment, we illustrate how constraints based on energy-dependent scattering can significantly differ from those based on an assumed constant cross-section. This highlights the importance of re-evaluating these constraints in the context of specific models.