Constraints on birefringence-free photon theory within standard model extensions

Constraints on the birefringence-free subset of Lorentz-violating (LV) operators are derived using 14 gamma-ray burst photons in the GeV band. These constraints target the isotropic c ( I ) 00 ( d ) coefficients for dimensions d = 6 , 8, 10 within the framework of the Standard-Model extension. Employing theory-agnostic Bayesian parameter estimation methods, our analysis indicates a preference for subluminal LV effects. Focusing on this case, we further refine the parameter constraints, yielding results that are mutually consistent. Within the 95% posterior credible interval, our constraints yield the bounds, | c ( I ) 00 ( 6 ) | ≤ 7.75 × 10 − 20 GeV − 2 , | c ( I ) 00 ( 8 ) | ≤ 4.92 × 10 − 24 GeV − 4 , and | c ( I ) 00 ( 10 ) | ≤ 3.46 × 10 − 28 GeV − 6 , which improve upon the most stringent credible-interval bounds reported in the literature by at least five orders of magnitude.