The discovery of the gamma-ray burst GRB 221009A is one of the most important observations in contemporary astrophysics. Not only is GRB 221009A an exceptionally bright and rare event estimated to occur once in 5000 years, but it is the gamma-ray burst observed at the highest energy so far. LHAASO detected GRB 221009A up to ∼15 TeV and Carpet even up to ∼300 TeV. Since within the standard propagation model photons are not expected to be observed above 10 TeV at the distance of GRB 221009A for any reasonable emission model—due to the interaction with background photons—such a detection also represents a milestone in the search for new physics. In the present review we show that two effects of new physics are indeed necessary to explain GRB 221009A. (1) Axion-like particles (ALPs) account for the LHAASO observations but are ineffective at Carpet energies. (2) Lorentz invariance violation (LIV) is instead complementary, being ineffective for LHAASO but explaining the Carpet detection. Therefore, GRB 221009A suggests a new physical ALP + LIV scenario in which photon-ALP oscillations take place in a LIV background.
Roncadelli et al. (Fri,) studied this question.