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 highenergy 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 / 4 1) dependence of the photon velocity on energy, we find a lower limit on the subluminal (superluminal) LIV scale of 5.9 & eth;6.2 & THORN; E p l . 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 1 / 4 2, corresponding to d 1 / 4 6 SME operators), the limits, which are currently the best available with the time -of -flight method, are 5.8 & eth;4.6 & THORN; x 10 -8 E pl . Our analysis uses the LHAASO data in the 0.2 -7 TeV range. Higher energy data would enable to improve our limits.