Professor Joseph Conlon

Abstract:

Axion-like particles (ALPs) and photons inter-convert in the presence of a magnetic field. At keV energies in the environment of galaxy clusters, the conversion probability can become unsuppressed for light ALPs. Conversion of thermal X-ray photons into ALPs can introduce a step-like feature into the cluster thermal bremsstrahlung spectrum, and we argue that existing X-ray data on galaxy clusters should be sufficient to extend bounds on ALPs in the low-mass region ma . 1 × 10−12 eV down to M ∼ 7 × 1011 GeV, and that for 1011 GeV < M . 1012 GeV light ALPs give rise to interesting and unique observational signatures that may be probed by existing and upcoming Xray (and potentially X-ray polarisation) observations of galaxy clusters.