# Sub-GeV Dark Matter in Superfluid He-4: an Effective Theory Approach

## TL;DR

This paper uses an effective field theory to analyze the potential for detecting sub-GeV dark matter via interactions with superfluid helium-4 phonons, providing a new theoretical framework for experimental searches.

## Contribution

It introduces an effective theory approach to calculate dark matter interactions with superfluid helium-4 phonons, enabling direct computation of emission rates and distributions.

## Key findings

- Large exclusion regions for sub-GeV dark matter masses.
- Effective field theory accurately predicts phonon emission rates.
- Method applicable to various dark matter models.

## Abstract

We employ an effective field theory to study the detectability of sub-GeV dark matter through its interaction with the gapless excitations of superfluid helium-4. In a quantum field theory language, the possible interactions between the dark matter and the superfluid phonon are solely dictated by symmetry. We compute the rate for the emission of one and two phonons, and show that these two observables combined allow for a large exclusion region for the dark matter masses. Our approach allows a direct calculation of the differential distributions, even though it is limited only to the region of softer phonon excitations, where the effective field theory is well defined. The method presented here is easily extendible to different models of dark matter.