Changes in extensive air showers from isotropic Lorentz violation in the photon sector

TL;DR

This paper investigates how isotropic Lorentz violation in the photon sector affects extensive air shower development, showing that faster photons lead to earlier shower maxima, which can be used to set tighter constraints on Lorentz violation.

Contribution

It introduces a model of Lorentz violation affecting photon velocities and predicts observable effects on air shower development, enabling improved experimental bounds.

Findings

Fast photons decay promptly into electron-positron pairs

Accelerated shower development reduces the atmospheric depth of maximum

Precise measurements can tighten constraints on Lorentz-violating parameters

Abstract

We consider a theory with isotropic nonbirefringent Lorentz violation in the photon sector and explore the effects on the development of the electromagnetic component of extensive air showers in the Earth atmosphere. Specifically, we consider the case of a "fast" photon with a phase velocity larger than the maximum attainable velocity of a massive Dirac fermion (this case corresponds to a negative Lorentz-violating parameter $\kappa$ in the action). Shower photons with above-threshold energies decay promptly into electron-positron pairs, instead of decaying by the conventional production of electron-positron pairs in the background fields of atomic nuclei. This rapid production of charged leptons accelerates the shower development, decreasing the atmospheric depth of the shower maximum ($X_\text{max}$) by an amount which could be measured by cosmic-ray observatories. Precise measurements of $X_\text{max}$ could then improve existing limits on the negative Lorentz-violating parameter $\kappa$ by several orders of magnitude.