Dark Matter Signatures in the Anisotropic Radio Sky

TL;DR

This paper explores the potential of using the anisotropic radio sky to detect dark matter annihilation signals, focusing on synchrotron emission characteristics and their distinguishability from astrophysical backgrounds.

Contribution

It provides a detailed calculation of the expected radio background from dark matter annihilation and compares it with astrophysical sources, highlighting the detectability with future radio telescopes.

Findings

Dark matter signals could be detectable at 2 GHz with current and future radio telescopes.

Dark matter-induced anisotropies are flatter than astrophysical backgrounds, aiding in their identification.

Radio source counts can also constrain dark matter properties.

Abstract

We calculate intensity and angular power spectrum of the cosmological background of synchrotron emission from cold dark matter annihilations into electron positron pairs. We compare this background with intensity and anisotropy of astrophysical and cosmological radio backgrounds, such as from normal galaxies, radio-galaxies, galaxy cluster accretion shocks, the cosmic microwave background and with Galactic foregrounds. Under modest assumptions for the dark matter clustering we find that around 2 GHz average intensity and fluctuations of the radio background at sub-degree scales allows to probe dark matter masses >100 GeV and annihilation cross sections not far from the natural values <sigma v> ~ 3 x 10^(-26) cm^3/s required to reproduce the correct relic density of thermal dark matter. The angular power spectrum of the signal from dark matter annihilation tends to be flatter than that from astrophysical radio backgrounds. Furthermore, radio source counts have comparable constraining power. Such signatures are interesting especially for future radio detectors such as SKA.