Multi-messenger probes of dark matter, from radio to multi-frequency

Abstract

The nature of dark matter remains one of the most significant problems in modern physics. One candidate hypothesis with strong theoretical motivation is a WIMP (Weakly Interacting Massive Particle) in the form of the supersymmetric neutralino. Although this lacks experimental evidence, supersymmetry may manifest in collider experiments and also has observable consequences in the emission of annihilation products from cosmic structures which would play host to large neutralino densities. Historically, interest has been focussed upon the direct detection of WIMPs, as well as indirect observation through -rays produced by pair-annihilation processes. In this work we present a detailed argument for a multi-frequency observational strategy. We motivate this by studying the redshift evolution of radio synchrotron radiation emitted by WIMP annihilation-product electrons. In so doing, we demonstrate the potential power of the SKA to probe the neutralino parameter space, being able to produce constraints several orders of magnitude better than current limits and distinguish between differing neutralino masses and annihilation channels. Furthermore, we motivate the SKA as a machine to study dark matter by discussing its ability to characterise cosmic magnetic fields through rotation measures and polarimetry, as well as resolve between non-thermal emissions produced by dark matter and those resulting from strictly baryonic processes, like star formation. These technical capabilities obviate the central uncertainties in the study of synchrotron radiation. Additionally, we highlight optimal laboratories for neutralino detection via the SKA, based on structures that might produce dark matter emissions with lower background synchrotron radiation. In particular we highlight galaxies and galaxy clusters at redshifts z 1 and local dwarf spheroidal galaxies. Finally, we demonstrate the potential of X-rays, through the ASTRO-H mission, to compliment the SKA in a multi-frequency search. We then demonstrate our multi-frequency approach in the analysis of several prominent claims of signals compatible with dark matter-induced emissions. Showing that models designed to account for the AMS-2/Fermi/PAMELA antiparticle and galactic centre -ray excesses are incompatible with existing data as well as demonstrating that a dark matter interpretation of the Reticulum-2 -ray excess is untenable for a wide range of dark matter particle masses.