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

Abstract

In this paper, we consider the impact of Lorentz Invariance Violation (LIV) on the γ − γ 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 γ − γ opacity for photons with energies 10 TeV. However, the effect is not expected to be sufficient to explain the apparent spectral hardening of several observed VHE γ-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 γγ 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 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.

Testing Lorentz Invariance Violation at the Pierre Auger Observatory

“…Identical and homogeneously distributed UHECR sources are considered emitting four different nuclear species ( 1 H, 4 He, 14 N, 28 Si) with an energy spectrum given by a power law with a broken exponential cutoff,…”

“…Potential LIV signatures are expected from several different astrophysical contexts. Previous studies have searched for LIV signals using distinct results, such as the time of flight of photons generated in gamma-ray bursts [2,3,4], modulations of the energy spectrum in TeV gamma-rays [5,6,7] and ultra-high energy cosmic rays (UHECR) [8,9], and upper limits on the flux of EeV photons [10,11]. No LIV signal has yet been found [1] and, thus, restrictive limits on the violation have been set [12].…”

Intergalactic γ-ray propagation: basic ideas, processes, and constraints

“…For especially high values of center-of-mass energy, additional processes also set in, such as muon pair production γγ → µ + µ − [6] and double pair production γγ → e + e − e + e − [7] for γ-rays. Additionally, there is a quest for New Physics processes, such as γ-axion-like particle (ALP) mixing [8]- [11] or Lorentz invariance violation (LIV) [13]- [15].…”

Extragalactic background light inhomogeneities and Lorentz-Invariance Violation in gamma-gamma absorption and Compton scattering

“…Even if we consider the combination of both effects (cosmic void along the line of sight and LIV) the reduction of the EBL gamma-gamma opacity is too small to explain the unexpectedly hard VHE gamma-ray spectra of some blazars. More detailed calculations considering a subluminal and a superluminal modification of the dispersion relation for photons for the LIV effect, by considering γγ absorption and also the impact of LIV effect on the Compton scattering process are presented in [30].…”