Abstract Very high energy (VHE; E ≳ 100 GeV) gamma rays are expected to experience strong attenuation during cosmological propagation due to electron–positron pair production on the extragalactic background light (EBL). Recent observations of GRB 221009A ( z = 0.151), including photons up to ∼18 detected by LHAASO and a ∼300 TeV event reported by Carpet-3, suggest a higher-than-expected transparency of the Universe at extreme energies. These observations cannot be explained by standard EBL absorption alone; moreover, neither Lorentz invariance violation (LIV) nor photon–axion-like particle (ALP) oscillations, when considered in isolation, appear sufficient to account for the survival of such photons over cosmological distances. In this work, we propose a joint propagation scenario that incorporates photon–ALP mixing in astrophysical magnetic fields together with subluminal quadratic LIV corrections to the γγ pair-production threshold. Applying this framework to the broadband gamma-ray spectrum of GRB 221009A, we show that ALPs with coupling ( g aγ = 1.685 × 10 −10 GeV −1 ) and mass ( m a = 9.545 × 10 −8 eV), combined with a quadratic LIV energy scale ( E LIV,2 = 1.30 × 10 −7 E Pl ) adopted from the literature, can significantly enhance the photon survival probability in the energy range (10–300) TeV. The resulting enhancement exceeds that obtained from either ALP mixing or LIV effects alone. These results indicate that a combined ALP–LIV scenario may provide a viable interpretation of the extreme-energy gamma-ray observations of GRB 221009A and highlight the potential of VHE gamma-ray measurements as probes of physics beyond the Standard Model.
Qin et al. (Fri,) studied this question.