# Circular polarisation: a new probe of dark matter and neutrinos in the sky

## TL;DR

This paper proposes that circular polarisation in X-ray and gamma-ray emissions could serve as a new indicator for dark matter and neutrino interactions, offering insights beyond traditional flux and spectrum analyses.

## Contribution

It introduces the concept that polarisation signals, specifically circular polarisation, can reveal properties of dark matter and neutrinos that are not accessible through flux measurements alone.

## Key findings

- Circular polarisation can be generated by neutrino decay and dark matter interactions.
- Polarisation signals could provide information on particle-antiparticle ratios and spatial distributions.
- Potential to uncover high-energy particle physics processes in astrophysical environments.

## Abstract

The study of anomalous electromagnetic emission in the sky is the basis of indirect searches for dark matter. It is also a powerful tool to constrain the radiative decay of active neutrinos. Until now, quantitative analyses have focused on the flux and energy spectrum of such an emission; polarisation has never been considered. Here we show that we could be missing out on an essential piece of information. The radiative decay of neutrinos, as well as the interactions of dark matter and neutrinos with Standard Model particles can generate a circular polarisation signal in X-rays or \gamma-rays. If observed, this could reveal important information about their spatial distribution and particle-antiparticle ratio, and could even reveal the nature of the high-energy particle physics processes taking place in astrophysical sites. The question of the observability of these polarised signatures and their separation from background astrophysical sources is left for future work.