Abstract:Up to date, there is no consensus regarding the origin of ultra high energy cosmic rays (UHECR) beyond the Greisen-Zatsepin-Kuzmin (GZK) limit. In order for these UHECR to reach the Earth, an extremely suppressed interaction between them and the cosmic microwave background (CMB) is required, which is impossible for standard model (SM) particles, except neutrinos. In this letter, we present constraints on the parameter space of models involving axion-like particles and dark photons, as candidates for UHECRs, by… Show more
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