Quantum gravity phenomenology induced in the propagation of UHECR, a kinematical solution in Finsler and generalized Finsler spacetime

TL;DR

This paper investigates how quantum gravity effects, modeled through Finsler geometry, can modify the propagation of ultra-high-energy cosmic rays, potentially explaining observed anomalies in their expected attenuation due to the GZK cut-off.

Contribution

It introduces a covariant framework using generalized Finsler spacetime to incorporate quantum gravity effects into UHECR kinematics, preserving Lorentz invariance.

Findings

Modified dispersion relations can dilate the GZK opacity horizon.

Lorentz covariance modifications relate to increased attenuation length.

Quantum spacetime geometry impacts cosmic ray propagation.

Abstract

It is well-known that the Universe is opaque to the propagation of Ultra-High-Energy Cosmic Rays (UHECRs) since these particles dissipate energy during their propagation interacting with the Cosmic Microwave Background (CMB) mainly in the so-called GZK cut-off phenomenon. Some experimental evidence seems to hint at the possibility of a dilation of the GZK predicted opacity sphere. It is well-known that kinematical perturbations caused by supposed quantum gravity (QG) effects can modify the foreseen GZK opacity horizon. The introduction of Lorentz Invariance Violation (LIV) can indeed reduce, in some cases making negligible, the CMB-UHECRs interaction probability. In this work we explore the effects induced by modified kinematics in the UHECRs phenomenology from the QG perspective. We explore the possibility of a geometrical description of the massive fermions interaction with the supposed quantum structure of spacetime in order to introduce a Lorentz covariance modifification. The kinematics is amended modifying the Dispersion Relations (DRs) of free particles in the context of a covariance-preserving framework. This spacetime description requires a more general geometry than the usual Riemannian one, indicating for instance the Finsler construction and the related generalized Finsler spacetime as ideal candidates. Finally we investigate the correlation between the magnitude of Lorentz covariance modification and the attenuation length of the photopion production process related to the GZK cut-off, demonstrating that the predicted opacity horizon can be dilated even in the context of a theory that does not require any privileged reference frame.