Predictions of Ultra-High Energy Cosmic Ray Propagation in the Context of Homogeneously Modified Special Relativity

TL;DR

This paper explores how a specific Lorentz Invariance Violation theory, Homogeneously Modified Special Relativity, affects the propagation and observable horizon of ultra-high-energy cosmic rays by modifying their interaction probabilities.

Contribution

It introduces a modified simulation framework to study the impact of HMSR on cosmic ray propagation and horizon size, providing new insights into LIV effects on UHECRs.

Findings

HMSR extends the proton opacity horizon for UHECRs.

The attenuation length for photopion production is significantly altered.

Simulation results suggest observable differences in cosmic ray fluxes at Earth.

Abstract

Ultra high energy cosmic rays (UHECRs) may interact with photon backgrounds and thus the universe is opaque to their propagation. Many Lorentz Invariance Violation (LIV) theories predict a dilation of the expected horizon from which UHECRs can arrive to Earth, in some case even making the interaction probability negligible. In this work, we investigate this effect in the context of the LIV theory that goes by the name of Homogeneously Modified Special Relativity (HMSR). In this work, making use of a specifically modified version of the Sim- Prop simulation program in order to account for the modifications introduced by the theory to the propagation of particles, the radius of the proton opacity horizon (GZK sphere), and the attenuation length for the photopion production process are simulated and the modifications of these quantities introduced by the theory are studied.