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Decaying axion-like particles (ALP) with masses in the eV range which mightoccupy dark matter halos of the Milky Way and other galaxies produce acharacteristic "bump" feature in the spectrum of extragalactic background light(EBL). This feature leaves an imprint on the gamma-ray spectra of distantextragalactic sources. We derive constraints on the ALP coupling to photonsbased on analysis of spectra of very-high-energy gamma-ray loud blazars. Wecombine gamma-ray spectral measurements by Fermi/LAT and Cherenkov telescopesand fit a model in which the intrinsic source spectrum is modified by pairproduction on photons produced by ALP decays. We constrain the amplitude ofgamma-ray flux suppression by this effect. We find that the combined Fermi/LATand VERITAS data set for the source 1ES 1218+304 currently provides thetightest constraint on ALP-two-photon coupling which is complementary to theconstraints imposed by non-observation of excess energy loss in HorizontalBranch stars, by the high-resolution spectroscopic observations of galaxyclusters with optical telescopes and by the searches of ALP signal with CERNSolar Axion Telescope. Our analysis favours existence of a bump in the EBLspectrum which could be produced by ALPs in the mass range 2-3 eV andaxion-photon coupling $\sim 10^{-10}$ GeV$^{-1}$. We discuss possibilities forverification of this hint with deeper Cherenkov telescope observations of largenumber of blazars with current generation instruments and with the CherenkovTelescope Array.

Search for decaying eV-mass axion-like particles using gamma-ray signal from blazars