Constraints on axion-like Particles from the high-energy Universe

The interaction of axion-like particles (ALPs) with two photons enable the oscillations between photons and ALPs in an external magnetic field. This interaction modify the energy spectrum of astrophysical sources under the form of an irregular behavior in a limited energy range. This signature is searched in the high-energy spectra of active galactic nuclei to put stringent constraints on the ALP coupling to photons