On the detectability of Lorentz invariance violation through anomalous multi-TeV $\gamma$-ray spectra of blazars

TL;DR

This paper explores how Lorentz invariance violation could alter the cosmic opacity for multi-TeV gamma rays from blazars, proposing high-energy blazar observations as a method to detect such quantum gravity effects.

Contribution

It derives a modified optical depth expression considering LIV effects and applies it to predict gamma-ray spectra of blazars, highlighting potential observational signatures.

Findings

LIV can reduce cosmic opacity for gamma rays above 10 TeV.

High-energy blazars like Mkn 501 and 1ES 0229+200 are promising LIV probes.

Hard intrinsic spectra of extreme BL Lacs make them suitable for LIV detection.

Abstract

Cosmic opacity for very high-energy gamma rays ($E>10$ TeV) due to the interaction with the extragalactic background light can be strongly reduced because of possible Lorentz-violating terms in the particle dispersion relations expected, e.g., in several versions of quantum gravity theories. We discuss the possibility to use very high energy observations of blazars to detect anomalies of the cosmic opacity induced by LIV, considering in particular the possibility to use -- besides the bright and close-by BL Lac Mkn 501 -- extreme BL Lac objects. We derive the modified expression for the optical depth of $\gamma$ rays considering also the redshift dependence and we apply it to derive the expected high-energy spectrum above 10 TeV of Mkn 501 in high and low state and the extreme BL Lac 1ES 0229+200. We find that, besides the nearby and well studied BL Lac Mkn 501 -- especially in high state --, suitable targets are extreme BL Lac objects, characterized by quite hard TeV intrinsic spectra likely extending at the energies relevant to detect LIV features.