New physics as a possible explanation for the Amaterasu particle

The Telescope Array experiment has recently reported the most energetic event detected in the hybrid technique era, with a reconstructed energy of 240 EeV, which has been named "Amaterasu" after the Shinto deity. Its origin is intriguing since no powerful enough candidate sources are located within the region consistent with its propagation horizon and arrival direction. In this work, we investigate the possibility of describing its origin in a scenario of new physics, specifically under a Lorentz Invariance Violation (LIV) assumption. The kinematics of UHECR propagation under a phenomenological LIV approach is investigated. The total mean free path for a particle with Amaterasu's energy increases from a few Mpc to hundreds of Mpc for -₇₀₃, ₀ > 10^-22, expanding significantly the region from which it could have originated. A combined fit of the spectrum and composition data of Telescope Array under different LIV assumptions was performed. The data is best fitted with some level of LIV both with and without Amaterasu. The improvement of the LIV fit is larger when Amaterasu is considered. New physics in the form of LIV could, thus, provide a plausible explanation for the Amaterasu particle.