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Extensions of the Standard Model of particles commonly predict the existenceof axion(-like) particles (ALPs) that could be detected through their couplingto photons in external magnetic fields. This coupling could lead tomodifications of $\gamma$-ray spectra from extragalactic sources. Above acertain energy, the $\gamma$-ray flux should be exponentially damped due to theinteraction with photons of background radiations fields. ALPs, on the otherhand, propagate unimpeded over cosmological distances and a reconversion into$\gamma$-rays could lead to an additional component in the spectra. Here, wepresent the sensitivity of the proposed Cherenkov Telescope Array (CTA) todetect this spectral hardening. Using the full instrumental response functionsof CTA, a combined likelihood analysis of four $\gamma$-ray sources shows thata significant detection of the ALP signal is possible for couplings$g_{a\gamma} \gtrsim 2\times10^{-11}\,\mathrm{GeV}^{-1}$ and ALP masses $m_a\lesssim 100\,\mathrm{neV}$. We discuss the dependency of these values ondifferent model assumptions and magnetic-field scenarios and identify the bestobservation strategy to search for an ALP induced boost of the $\gamma$-rayflux.

Sensitivity of the Cherenkov Telescope Array to the detection of axion-like particles at high gamma-ray opacities