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

Understand

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.