Dark matter-electron scattering in dielectrics

TL;DR

This paper introduces a dielectric response-based framework for dark matter-electron scattering, accounting for in-medium screening effects, which impacts the sensitivity of dielectric-based direct detection experiments.

Contribution

It presents a novel formulation that incorporates screening effects into dark matter-electron scattering calculations using dielectric responses, improving upon previous models.

Findings

Screening effects significantly reduce detection sensitivity.

Both scalar and vector mediators are affected by screening.

Different dielectric response models yield consistent results.

Abstract

A number of direct detection experiments are searching for electron excitations created by scattering of sub-GeV dark matter. We present an alternate formulation of dark matter-electron scattering in terms of the dielectric response of a material. For dark matter which couples to electrons, this approach automatically accounts for in-medium screening effects, which were not included in previous rate calculations for semiconductor targets. We show that the screening effects appear for both scalar and vector mediators. The result is a non-negligible reduction of reach for direct detection experiments which use dielectric materials as targets. We also explore different determinations of the dielectric response, including first-principles density functional theory (DFT) calculations and a data-driven analytic approximation using a Mermin oscillator model.