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

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.