Scalar Direct Detection: In-Medium Effects

TL;DR

This paper investigates how in-medium effects alter the detection sensitivity of light scalar dark matter in direct detection experiments, revealing that some setups are less effective while others remain promising, especially for boosted scalars.

Contribution

It introduces a thermal field theory approach to account for in-medium effects on scalar DM detection, highlighting the importance of these effects and identifying promising experimental setups.

Findings

In-medium effects significantly reduce the sensitivity of many direct detection experiments.

Dirac materials and tunable plasma haloscopes are promising for scalar DM detection.

Boosted scalar DM from astrophysical sources is less affected by in-medium suppression.

Abstract

A simple extension of the Standard Model consists of a scalar field that can potentially constitute the dark matter (DM). Significant attention has been devoted to probing light $\mathcal{O}(\lesssim 10~\rm{eV})$ scalar DM, with a multitude of experimental proposals based on condensed matter systems as well as novel materials. However, the previously overlooked effective in-medium mixing of light scalars with longitudinal plasmons can strongly modify the original sensitivity calculations of the direct detection experiments. We implement the in-medium effects for scalar DM detection, using thermal field theory techniques, and show that the reach of a large class of direct DM detection experiments searching for light scalars is significantly reduced. This development identifies setups based on Dirac materials and tunable plasma haloscopes as particularly promising for scalar DM detection. Further, we also show that scalars with significant boost with respect to halo DM, such as those produced in the Sun, decay of other particles or by cosmic rays, will not suffer from in-medium suppression. Hence, multi-tonne direct DM detection experiments, such as those based on xenon or argon, also constitute a favorable target. We also discuss scalar mediated DM scattering.