300 TeV photon from GRB 221009A: A hint at nonlinear Lorentz invariance violation?

The air shower array Carpet-3 detected a 300 TeV photon from the direction of GRB 221009A at 4536 s after the Fermi Gamma-ray Burst Monitor trigger for this event. If the association with this gamma-ray burst is real, then it poses two puzzles. First, why was this photon not absorbed by the extragalactic background light? “New physics” beyond the Standard Model is required to explain how it managed to reach Earth from a cosmological distance. Second, why was this photon detected when the very high energy (VHE) afterglow observed by the Large High Altitude Air Shower Observatory (LHAASO) already faded? A novel astrophysical mechanism is required to explain this delay. In this work we show that Lorentz invariance violation (LIV), which arises as a low-energy limit of certain quantum gravity theories, can solve both puzzles. It shifts thresholds of particle interaction and changes the opacity of the extragalactic background, and causes energy-dependent variations of the photon velocity, which changes the photon time of flight. We investigate the LIV parameter space assuming that the 300 TeV photon is a part of the VHE afterglow detected by the LHAASO in the TeV range. We identify viable solutions and place stringent two-sided constraints on the LIVenergy scale required to resolve the observational puzzles. First-order LIV appears to be incompatible with the constraints set by analyzing the TeVafterglow of this gamma-ray burst. Viable solutions emerge for higher orders. In particular, the commonly studied secondorder subluminal LIV with (Formula presented.) (95.4% credibility level; E_PlM is the Planck energy) is consistent with all the observed data.