A new H.E.S.S. publication has just appeared in the Journal of Cosmology and Astroparticle Physics. For this study, we have investigated how the spectra of a class of distant gamma-ray emitters – called blazars – are modified by the interaction of gamma rays with the extragalactic background light (EBL), i.e. low-energy photons that fill the space between us and the gamma-ray source. Specifically, we looked into how this absorption feature could be changed due to the presence of a heavy, axion-like particle, or ALP for short. This hypothetical particle has been suggested to solve a theoretical problem in particle physics called the strong CP problem and is also a promising candidate for dark matter. With our work, we are able to constrain the coupling between ALPs and photons. Our limits are competitive with other existing constraints, while providing a complementary approach.

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Journal reference: Journal of Cosmology and Astroparticle Physics 10(2026)005