Modelling $\gamma$-ray-axion-like particle oscillations in turbulent magnetic fields: relevance for observations with Cherenkov telescopes

Abstract

Axion-like particles (ALPs) are a common prediction of certain theories beyond the Standard Model and couple to photons in the presence of external magnetic fields. As a consequence, photon-ALP conversions could lead to an enhancement of the flux of extragalactic gamma-ray sources that is otherwise attenuated due to the interactions with background radiation fields. The magnetic fields traversed by the gamma rays are often turbulent and frequently modelled with a simple domain-like structure. Given a maximum mixing between photons and ALPs, we show that in such models realisations of the fields exist for which the photon-ALP oscillation probability vanishes. This behaviour does not occur in more sophisticated magnetic-field models.