Lorentz invariance violation limits from GRB 221009A

It has been long conjectured that a signature of quantum gravity will be Lorentz invariance violation (LIV) that could be observed at energies much lower than the Planck scale. One possible signature of LIV is an energy-dependent speed of photons. This can be tested with a distant transient source of very high-energy photons. We explore time-of-flight limits on LIV derived from LHAASO's observations of tens of thousands of TeV photons from GRB 221009A, the brightest gamma-ray burst of all time. For a linear ($n=1$) dependence of the photon velocity on energy, we find a lower limit on the subluminal (superluminal) LIV scale of 5.9(6.2)Eₚₗ. These are comparable to the stringent limits obtained so far and as an independent bound obtained from a different redshift confirm their robustness. For a quadratic model ($n=2$, corresponding to $d=6$ SME operators), the limits, which are currently the best available with the time-of-flight method, are 5.8(4.6)×10^-8Eₚₗ. Our analysis uses the LHAASO data in the 0.2--7 TeV range. Higher energy data would enable to improve our limits.