Parton-model calculation of a nonstandard decay process in isotropic modified Maxwell theory

TL;DR

This paper calculates a nonstandard decay process in isotropic modified Maxwell theory using the parton model, refining decay rate estimates while confirming existing bounds on Lorentz violation from cosmic ray observations.

Contribution

It introduces a parton-model approach to evaluate decay rates in modified Maxwell theory, updating previous point-particle results and confirming bounds on Lorentz-violating parameters.

Findings

Decay rate estimates are refined by about an order of magnitude.

Upper bound on Lorentz violation parameter $$ remains at 10^{-19}.

Lower bound on $$ from gamma-ray data is at -10^{-15}.

Abstract

We have performed a calculation in the parton-model approximation of a nonstandard decay process in isotropic modified Maxwell theory coupled to standard Dirac theory, with a single Lorentz-violating parameter $\kappa$ in the photonic sector. Previous calculations of this process (vacuum Cherenkov radiation by a proton for the theory with $\kappa>0$) were performed for pointlike particles, and an upper bound on $\kappa$ at the $10^{-19}$ level was obtained from experimental data on ultra-high-energy cosmic rays. The parton-model results change the decay rate by about an order of magnitude but give the same upper bound on $\kappa$ because the threshold energy is unchanged. The previous point-particle calculation of photon decay into an electron-positron pair for the theory with $\kappa<0$ remains valid, and experimental results on cosmic gamma rays provide a lower bound on $\kappa$ at the $-10^{-15}$ level.