Lorentz violation effects on astrophysical propagation of very high energy photons

TL;DR

This paper reviews how Lorentz violation, predicted by some quantum gravity theories, affects the propagation of high-energy astrophysical photons, discussing observational effects, recent experimental constraints, and implications for quantum gravity models.

Contribution

It provides a comprehensive review of theoretical predictions and experimental results on Lorentz violation effects on high-energy photon propagation, including new classifications and recent constraints.

Findings

Lorentz violation causes observable time lags and spectral modifications in high-energy photons.

Current and upcoming instruments can test Lorentz violation effects.

Recent constraints from ultra-high energy cosmic rays limit Lorentz violation parameters.

Abstract

Lorentz violation (LV) is predicted by some quantum gravity (QG) candidates, wherein the canonical energy-momentum dispersion relation, $E^2=p^2+m^2$, is modified. Consequently, new phenomenons beyond the standard model are predicted. Especially, the presence of LV highly affects the propagation of astrophysical photons with very high energies from distant galaxies. In this paper, we review the updating theoretical and experimental results on this topic. We classify the effects into three categories: (i) time lags between photons with different energies; (ii) a cutoff of photon flux above the threshold energy of photon decay, $\gamma \rightarrow e^++e^-$; (iii) new patterns in the spectra of multi-TeV photons and EeV photons, due to the absorption of background lights. As we can see, the details of LV effects on astrophysical photons depend heavily on the "phase space" of LV parameters. From observational aspects, nowadays available and upcoming instruments can study these phenomenons hopefully, and shed light onto LV issues and QG theories. The most recent progresses and constraints on the ultra-high energy cosmic rays (UHECRs) are also fully discussed.