Direct Detection of Mechanism-Agnostic Fast-Moving Dark Matter

TL;DR

This paper develops a comprehensive, model-independent framework for interpreting electron recoil signals caused by fast-moving dark matter, incorporating relativistic effects and atomic physics to enhance detection strategies across various experiments.

Contribution

It introduces a novel, relativistic formalism for analyzing electron recoil signals from boosted dark matter, applicable across multiple models and experimental setups.

Findings

Atomic effects are negligible at high recoil energies.

The framework enables accurate predictions of differential cross sections.

It highlights the complementarity of detection methods for relativistic dark matter.

Abstract

We present a comprehensive framework for interpreting electron recoil signals induced by fast-moving dark matter (DM), applicable across a wide range of theoretically motivated models. Amid both null results in conventional weakly interacting massive particle searches and growing interest in alternative DM scenarios, we focus on (semi-)relativistic DM components that can arise from mechanisms such as DM annihilation, decay, or cosmic-ray acceleration. These boosted DM candidates produce distinct experimental signatures that differ qualitatively from non-relativistic DM, necessitating a dedicated treatment. Our framework incorporates relativistic kinematics and atomic effects through ionization form factors, enabling accurate predictions of differential cross sections in both low- and high-energy regimes. We demonstrate how atomic effects become negligible at high recoil energies, validating the free-electron approximation in specific parameter regions. Furthermore, we highlight the complementarity between low-threshold direct detection experiments and high-threshold neutrino observatories in probing fast-moving DM across broad kinematic domains. This formalism provides a robust and model-independent foundation for interpreting current and future searches for relativistic DM.