Addendum: Ultrahigh-energy cosmic-ray bounds on nonbirefringent modified-Maxwell theory

TL;DR

This paper derives stringent bounds on nine parameters of a modified-Maxwell theory using ultrahigh-energy cosmic-ray observations, constraining deviations from standard electromagnetism.

Contribution

It provides the first precise bounds on nonbirefringent modified-Maxwell parameters using UHECR data, improving previous limits significantly.

Findings

Two-sided bounds on eight nonisotropic parameters at 10^{-18} level

One-sided bound on isotropic parameter at 10^{-19} level

Constraints imply no detectable vacuum Cherenkov radiation from UHECRs

Abstract

Nonbirefringent modified-Maxwell theory, coupled to standard Dirac particles, involves nine dimensionless parameters, which can be bounded by the inferred absence of vacuum Cherenkov radiation for ultrahigh-energy cosmic rays (UHECRs). With selected UHECR events, two-sided bounds on the eight nonisotropic parameters are obtained at the 10^{-18} level, together with an improved one-sided bound on the single isotropic parameter at the 10^{-19} level.