Abstract
In extensive air showers induced by ultra-high-energy (UHE) cosmic rays, secondary photons are expected to be produced at energies far above those accessible by other means. It has been shown that the decay of such photons, as possible in certain theories allowing Lorentz violation, can lead to significant changes of the shower development. Based on observations of the average depth of the shower maximum $\left<X_\text{max}\right>$, a stringent bound on Lorentz violation has been placed in a previous work. Here we include the shower-to-shower fluctuations $\sigma(X_\text{max})$ as an additional observable. The combined comparison of $\left<X_\text{max}\right>$ and $\sigma(X_\text{max})$ to shower observations allows a much stricter test of the possible decay of UHE photons, improving the previous bound by a factor of 50.
Highlights
In current efforts toward a more fundamental theory in particle physics, deviations from exact Lorentz symmetry may occur
We focus on isotropic, nonbirefringent Lorentz violation (LV) in the photon sector
A full Monte Carlo (MC) ansatz was used in [6] to study the impact of LV on air showers initiated by primary hadrons
Summary
In current efforts toward a more fundamental theory in particle physics, deviations from exact Lorentz symmetry may occur (see e.g., [1]). The impact of this type of LV on extensive air showers initiated by cosmic rays in the Earth’s atmosphere is exploited, with a focus on ultrahigh energies (UHE) above 1 EeV 1⁄4 1018 eV. This approach was first studied in [8], where an analytical ansatz was used, modifying the well-known Heitler model for electromagnetic cascades to include LV through photon decay. A big impact on the longitudinal shower development of electromagnetic cascades was found Building upon this idea, a full Monte Carlo (MC) ansatz was used in [6] to study the impact of LV on air showers initiated by primary hadrons.
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