New two-sided bound on the isotropic Lorentz-violating parameter of modified Maxwell theory

TL;DR

This paper derives a new, highly precise two-sided bound on the Lorentz-violating parameter in modified Maxwell theory by analyzing cosmic-ray and gamma-ray observations, significantly improving previous laboratory bounds.

Contribution

It provides the first two-sided bound on the isotropic Lorentz-violating parameter kappa_tr using astrophysical data, surpassing laboratory bounds by eight orders of magnitude.

Findings

No vacuum Cherenkov radiation observed in cosmic-ray data.

No photon decay observed in gamma-ray data.

Established a two-sided bound on kappa_tr from astrophysical observations.

Abstract

There is a unique Lorentz-violating modification of the Maxwell theory of photons, which maintains gauge invariance, CPT, and renormalizability. Restricting the modified-Maxwell theory to the isotropic sector and adding a standard spin-one-half Dirac particle p^\pm with minimal coupling to the nonstandard photon \widetilde{\gamma}, the resulting modified-quantum-electrodynamics model involves a single dimensionless "deformation parameter," \widetilde{\kappa}_{tr}. The exact tree-level decay rates for two processes have been calculated: vacuum Cherenkov radiation p^\pm \to p^\pm \widetilde{\gamma} for the case of positive \widetilde{\kappa}_{tr} and photon decay \widetilde{\gamma} \to p^+ p^- for the case of negative \widetilde{\kappa}_{tr}. From the inferred absence of these decays for a particular high-quality ultrahigh-energy-cosmic-ray event detected at the Pierre Auger Observatory and an excess of TeV gamma-ray events observed by the High Energy Stereoscopic System telescopes, a two-sided bound on \widetilde{\kappa}_{tr} is obtained, which improves by eight orders of magnitude upon the best direct laboratory bound. The implications of this result are briefly discussed.