Using Ultrahigh-Energy Cosmic Rays and Air Showers to Test Lorentz Invariance Within Modified Maxwell Theory

Abstract

Cosmic rays and air showers at ultra-high energy are unique tools to test the validity of Lorentz invariance. A brief overview is given on such tests focusing on isotropic, non-birefringent Lorentz violation (LV) in the photon sector. Based on the apparent absence of vacuum Cherenkov radiation and photon decay, the LV parameter $\kappa$ is bound to $-0.6 \cdot 10^{-20}<\kappa<6 \cdot 10^{-20}$ (98\% CL). We report an updated limit from cosmic-ray photon observations and preliminary results on testing vacuum Cherenkov radiation in air showers.