The effect of photon-axion-like particle conversions in galaxy clusters on very high energy {\gamma}-ray spectra

TL;DR

This paper investigates how photon-axion-like particle conversions in galaxy clusters and the Milky Way magnetic fields can enhance very high energy gamma-ray fluxes and reduce cosmic opacity, impacting observations of extragalactic sources.

Contribution

It demonstrates that photon-ALP oscillations can significantly modify VHE gamma-ray spectra, providing a potential explanation for observed spectral features.

Findings

Photon-ALP conversions can increase VHE gamma-ray fluxes.

Spectral hardening due to ALPs reduces universe opacity to gamma rays.

Magnetic fields in galaxy clusters and the Milky Way influence these effects.

Abstract

Very high energy (VHE, energy >~ 100 GeV) {\gamma}-rays originating from extragalactic sources interact with low energy photons of background radiation fields and produce electron-positron pairs. Alternatively, in the presence of ambient magnetic fields, they can convert into hypothetical axion-like particles (ALPs), pseudo-scalar spin-0 bosons, predicted by extensions of the standard model. These particles propagate unimpeded over cosmological distances. Here, the effect of photon-ALP oscillations in magnetic fields of galaxy clusters and the Milky Way on VHE {\gamma}-ray spectra is studied. It is shown that this mechanism can lead to a substantial enhancement of the VHE flux and a spectral hardening, thus effectively reducing the opacity of the Universe to VHE {\gamma}-rays.