Excitonic contributions to dark matter-electron scattering

TL;DR

This paper investigates how excitonic effects influence dark matter-electron scattering predictions in detector materials, finding significant impact in NaI but minimal in GaAs, thereby refining detection sensitivity estimates.

Contribution

It provides the first detailed comparison of excitonic effects on dark matter-electron scattering rates in NaI and GaAs using advanced many-body perturbation theory.

Findings

Excitonic effects significantly increase scattering rates in NaI at low energies.

In GaAs, excitonic effects have minimal impact on scattering predictions.

Results improve understanding of detector material responses to dark matter interactions.

Abstract

We determine whether excitonic effects affect predictions of dark matter (DM)-electron scattering rates by calculating the energy- and momentum-dependent energy-loss function, including electron-hole interaction excitonic effects, for the dark-matter scintillating detector materials GaAs and NaI. By comparing our results using the Bethe-Salpeter equation in the framework of many-body perturbation theory, which explicitly includes excitonic effects, with those using the quasiparticle random-phase approximation, which includes only electron-electron interaction and crystal local-field effects, we find that excitonic effects in NaI significantly increase the predicted scattering rate at low energy and as a result improve the cross-section sensitivity considering a realistic background. In contrast, the predicted scattering rate and the DM-electron scattering cross-section for GaAs are minimally affected by excitonic effects.