Ping He, Bo-Qiang Ma

Since the early reports of events beyond the Greisen-Zatsepin-Kuzmin (GZK) cutoff, the investigation of ultrahigh-energy cosmic rays has emerged as a fundamental method for testing Lorentz Invariance violation (LV) effects. Recent advances in observational capabilities have resulted in more stringent constraints on LV parameters. This study delves into the potentially anomalous phenomena arising from subluminal and superluminal LV effects, encompassing aspects such as proton decay and atypical threshold behavior of photo-pion production from protons within the GZK region. High-energy proton observations in cosmic rays have imposed stringent constraints on superluminal proton LV effects, while the confirmation of the GZK cutoff has established a robust boundary for the anomalous phenomena associated with subluminal proton LV effects. The research provides rigorously bilateral constraints on proton LV effects from both subluminal and superluminal standpoints.