Lorentz Invariance Violation Effects on Gamma-Gamma Absorption and Compton Scattering

TL;DR

This paper investigates how Lorentz Invariance Violation (LIV) could alter gamma-ray interactions like gamma-gamma absorption and Compton scattering, finding limited impact on observable astrophysical phenomena.

Contribution

It provides the first analysis of LIV effects on Compton scattering and compares LIV's impact on gamma-ray opacity with cosmic inhomogeneities.

Findings

LIV can significantly reduce gamma-gamma opacity for photons above 10 TeV in the subluminal case.

LIV effects on Compton scattering are only relevant at energies exceeding 1 PeV.

Superluminal LIV increases gamma-gamma opacity and reduces Klein-Nishina suppression, but likely lacks astrophysical significance.

Abstract

In this paper, we consider the impact of Lorentz Invariance Violation (LIV) on the $\gamma-\gamma$ opacity of the Universe to VHE-gamma rays, compared to the effect of local under-densities (voids) of the Extragalactic Background Light, and on the Compton scattering process. Both subluminal and superluminal modifications of the photon dispersion relation are considered. In the subluminal case, LIV effects may result in a significant reduction of the $\gamma-\gamma$ opacity for photons with energies $\gtrsim 10$ TeV. However, the effect is not expected to be sufficient to explain the apparent spectral hardening of several observed VHE $\gamma$-ray sources in the energy range from 100 GeV - a few TeV, even when including effects of plausible inhomogeneities in the cosmic structure. Superluminal modifications of the photon dispersion relation lead to a further enhancement of the EBL $\gamma\gamma$ opacity. We consider, for the first time, the influence of LIV on the Compton scattering process. We find that this effect becomes relevant only for photons at ultra-high energies, $E \gtrsim 1$ PeV. In the case of a superluminal modification of the photon dispersion relation, both the kinematic recoil effect and the Klein-Nishina suppression of the cross section are reduced. However, we argue that the effect is unlikely to be of astrophysical significance.