Constraints on birefringence-free photon theory within standard-model extension

Constraints on the birefringence-free subset of Lorentz-violating (LV) operators are derived using 14 GRB 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 (SME). 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, $|c_{(I)00}^{(6)}|\le7.75 \times 10^{-20} ~ {\rm GeV}^{-2}$, $|c_{(I)00}^{(8)}|\le4.92 \times 10^{-24} ~ {\rm GeV}^{-4}$, and $|c_{(I)00}^{(10)}|\le3.46 \times 10^{-28} ~ {\rm GeV}^{-6}$, which improve upon the most stringent credible-interval bounds reported in the literature by at least five orders of magnitude.

💡 Research Summary

The paper investigates Lorentz‑violating (LV) effects in the photon sector of the Standard‑Model Extension (SME) by focusing exclusively on the birefringence‑free subset of operators. In this subset, CPT‑odd coefficients and the Weyl‑type non‑metric part are set to zero, leaving only ten CPT‑even, parity‑even, spin‑weight‑zero coefficients denoted (\hat c_{F}^{\mu\nu}). These coefficients modify the photon dispersion relation at leading order to
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