Constraining the axion-photon coupling using radio data of the Bullet Cluster

TL;DR

This study uses radio observations of the Bullet Cluster to set new, tighter constraints on the axion-photon coupling constant for axion masses around 20 microelectronvolts, improving upon previous limits.

Contribution

It demonstrates that galaxy cluster radio data can effectively constrain axion dark matter properties, providing tighter bounds than existing experiments like CAST.

Findings

Upper limit on axion-photon coupling: $10^{-12}$ to $10^{-11}$ GeV$^{-1}$

Constraints are tighter than those from CAST for $m_a \,\sim\, 20$ $\mu$eV

Radio data from galaxy clusters is a powerful tool for axion searches.

Abstract

Axion is one of the most popular candidates of the cosmological dark matter. Recent studies considering the misalignment production of axions suggest some benchmark axion mass ranges near $m_a \sim 20$ $\mu$eV. For such axion mass, the spontaneous decay of axions can give photons in radio band frequency $\nu \sim 1-3$ GHz, which can be detected by radio telescopes. In this article, we show that using radio data of galaxy clusters would be excellent to constrain axion dark matter. Specifically, by using radio data of the Bullet cluster (1E 0657-55.8), we find that the upper limit of the axion-photon coupling constant can be constrained to $g_{a \gamma \gamma} \sim 10^{-12}-10^{-11}$ GeV$^{-1}$ for $m_a \sim 20$ $\mu$eV, which is tighter than the limit obtained by the CERN Axion Solar Telescope (CAST).