Searching for relativistic axions in the sky

TL;DR

This paper proposes using the SKA radio telescope to detect relativistic axions from dark matter decays, potentially exploring new parameter space beyond current constraints, especially for axions lighter than 10^{-13} eV.

Contribution

It demonstrates that SKA observations of dwarf galaxy Seg I can significantly improve axion detection sensitivity, accounting for magnetic turbulence and Bose enhancement effects.

Findings

SKA can probe axion parameter space beyond stellar and cosmological constraints.

Sensitivity is several orders of magnitude better than planned axion experiments.

Uncertainties due to magnetic turbulence and Bose enhancement are analyzed.

Abstract

Relativistic axions produced in decays of ${\mathcal O}(10^{-7}-10^{-2}$ $\text{eV})$ dark matter (DM) partially convert to photons after traversing the galactic magnetic field, giving rise to a signal observable by the Square Kilometer Array (SKA) radio telescope. We show that for axions lighter than a few $\times$ $10^{-13}$ eV a 100 h SKA observation of the local dwarf galaxy Seg I would probe parameter space not constrained by stellar cooling and cosmological observations, with sensitivity several orders of magnitude better than the planned dedicated axion dark matter search experiments. We quantify the uncertainties in the SKA sensitivity projections due to two effects that enhance the radio flux: the presence of turbulent magnetic fields inside the galaxy, and the Bose enhancement of the DM decays to axions, where the latter, in particular, warrants further study.