UHECRs Beyond the GZK Limit as Magnetic Monopole Candidates

A recent event in Ultra High Energy Cosmic Rays (UHECRs) known as the Amaterasu particle is the foundation of a possible glimpse into beyond the standard model physics. The particle was detected by the Telescope Array Project in 2021 and later identified in 2023 with an energy exceeding 240 EeV. There exists a limit that applies to protons as UHECRs known as the GZK limit. It is derived by calculating the mean free path of interactions between a proton and the CMB. The GZK limit is approximately 50 EeV with a mean free path of approximately 6 Mpc. Every time one of these collisions occur, the proton loses approximately 20% of its energy. Another fact that makes the Amaterasu particle interesting is that its arrival direction was calculated to be coming from the local void, a region of space with an under-density of galaxies relative to the rest of the Universe. This makes it unlikely for the Amaterasu particle to have been produced anywhere in the local void since there are no obvious sources. This also means that if we consider the Amaterasu particle to be a proton which crossed the local void, the energies with which it would have to be produced would be above ~10^23 eV. This is extremely unlikely given known acceleration mechanisms. We hypothesize that the Amaterasu particle is not a proton/nucleus, but a Magnetic Monopole (MM).