Extragalactic photon--axion-like particle oscillations up to 1000 TeV

TL;DR

This paper analyzes how axion-like particles (ALPs) influence high-energy photon propagation from distant blazars, incorporating recent observations of photon dispersion on the CMB, and predicts testable signals for upcoming gamma-ray observatories and experiments.

Contribution

It provides an exact calculation of photon survival probabilities considering ALPs and CMB effects, extending previous models to higher energies up to 1000 TeV.

Findings

Photon survival probability varies with energy and redshift.

Predicted signals are testable by future gamma-ray observatories.

ALPs could be detected in upcoming laboratory experiments.

Abstract

Axion-like particles (ALPs) are attracting increasing interest since, among other things, they are a prediction of many extensions of the standard model of elementary particles physics and in particular of superstrings and superbranes. Remarkably, depending on the set of their parameter space, they strongly increase the photon transparency in the very-high energy band. The recent discovery of photon dispersion on the CMB requires a substantial modification of the previous picture: this is indeed the goal of the present paper. We compute the photon survival probability from a blazar to us exactly, and we plot it versus the observed energy for 7 simulated blazars at different $z$ and 4 values of a model parameter. Our predictions can be tested by the new generation of $\gamma$-ray observatories like CTA, HAWC, GAMMA-400, LHAASO, TAIGA-HiSCORE and HERD. Finally, for our guessed values of $m_a$ and $g_{\gamma \gamma a}$ our ALP can be detected in the upgrade of ALPS II at DESY, the planned experiments IAXO, STAX and ABRACADABRA as well as with other techniques.