Ultrahigh-energy photons from LHAASO as probes of Lorentz symmetry violations

TL;DR

This paper discusses how ultra-high-energy photons detected by LHAASO can be used to test and constrain Lorentz symmetry violations, providing insights into quantum gravity models and potential new physics at near-Planckian energies.

Contribution

It proposes using LHAASO's photon observations to set new constraints on Lorentz violation frameworks and suggests future tests involving extragalactic PeV photons and threshold anomalies.

Findings

Detection of PeV photons constrains superluminal Lorentz violation.

Current observations may hint at subluminal Lorentz violation near the Planck scale.

Proposes future experiments to test Lorentz violation via pair-production thresholds.

Abstract

The Large High Altitude Air Shower Observatory~(LHAASO) is one of the most sensitive gamma-ray detector arrays currently operating at TeV and PeV energies. Recently the LHAASO experiment detected ultra-high-energy~(UHE; $E_{\gamma}\gtrsim 100~\mathrm{TeV}$) photon emissions up to $1.4~\mathrm{PeV}$ from twelve astrophysical gamma-ray sources. We point out that the detection of cosmic photons at such energies can constrain the photon self-decay motivated by superluminal Lorentz symmetry violation~(LV) to a higher level, thus can put strong constraints to certain LV frameworks. Meanwhile, we suggest that the current observation of the PeV-scale photon with LHAASO may provide hints to permit a subluminal type of Lorentz violation in the proximity of the Planckian regime, and may be compatible with the light speed variation at the scale of $3.6\times 10^{17}~\mathrm{GeV}$ recently suggested from gamma-ray burst~(GRB) time delays. We further propose detecting PeV photons coming from extragalactic sources with future experiments, based on LV-induced threshold anomalies of $e^{+}e^{-}$ pair-production, as a crucial test of subluminal Lorentz violation. We comment that these observations are consistent with a D-brane/string-inspired quantum-gravity framework, the space-time foam model.