Dark matter scattering in astrophysical media: collective effects

TL;DR

This paper demonstrates that collective effects in dense stellar media significantly influence dark matter scattering rates, affecting detection prospects and requiring their systematic inclusion in astrophysical models.

Contribution

It introduces a systematic method to incorporate collective effects into dark matter scattering calculations within stars, revealing their impact on observational signatures.

Findings

Collective effects can enhance or suppress dark matter scattering rates.

Scattering rates can differ by orders of magnitude for dark matter masses below 100 MeV.

Effects are significant even in dilute media like the Solar core.

Abstract

It is well-known that stars have the potential to be excellent dark matter detectors. Infalling dark matter that scatters within stars could lead to a range of observational signatures, including stellar heating, black hole formation, and modified heat transport. To make robust predictions for such phenomena, it is necessary to calculate the scattering rate for dark matter inside the star. As we show in this paper, for small enough momentum transfers, this requires taking into account collective effects within the dense stellar medium. These effects have been neglected in many previous treatments; we demonstrate how to incorporate them systematically, and show that they can parametrically enhance or suppress dark matter scattering rates depending on how dark matter couples to the Standard Model. We show that, as a result, collective effects can significantly modify the potential discovery or exclusion reach for observations of compact objects such as white dwarfs and neutron stars. While the effects are more pronounced for dark matter coupling through a light mediator, we show that even for dark matter coupling via a heavy mediator, scattering rates can differ by orders of magnitude from their naive values for dark matter masses <~ 100 MeV. We also illustrate how collective effects can be important for dark matter scattering in more dilute media, such as the Solar core. Our results demonstrate the need to systematically incorporate collective effects in a wide range of astroparticle contexts; to facilitate this, we provide expressions for in-medium self-energies for a variety of different media, which are applicable to many other processes of interest (such as particle production).