Dark matter signatures in the anisotropic radio sky

Abstract

We calculate the intensity and the angular power spectrum of the cosmological backgroundof synchrotron emission from cold dark matter annihilations into electron–positron pairs.We compare this background with the intensity and anisotropy of astrophysicaland cosmological radio backgrounds, such as those from normal galaxies, radiogalaxies and galaxy cluster accretion shocks, with the cosmic microwave backgroundand with Galactic foregrounds. Under modest assumptions for the dark matterclustering we find that around 2 GHz average intensity and fluctuations of the radiobackground at sub-degree scales allow us to probe dark matter masses GeV and annihilation cross sections not far from the natural values required to reproduce the correct relic density of thermal dark matter. The angular powerspectrum of the signal from dark matter annihilation tends to be flatter than that fromastrophysical radio backgrounds. Furthermore, radio source counts have comparableconstraining power. Such signatures are interesting, especially for future radio detectorssuch as SKA.