Limits on light-speed anisotropies from Compton scattering of high-energy electrons

TL;DR

This study uses high-energy Compton scattering data to set the most stringent limits to date on possible anisotropies in the speed of light, constraining Lorentz violation parameters within the Standard-Model Extension.

Contribution

It provides the first non-threshold collision-kinematics constraint on Lorentz violation using Compton-edge photon energy measurements.

Findings

Sets a 95% confidence limit of 1.6 x 10^{-14} on Lorentz violation parameters

Improves previous bounds on light-speed anisotropies by an order of magnitude

Uses sidereal variation analysis of Compton scattering data

Abstract

The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the ESRF's GRAAL facility constrains such anisotropies representing the first non-threshold collision-kinematics study of Lorentz violation. When interpreted within the minimal Standard-Model Extension, this result yields the two-sided limit of 1.6 x 10^{-14} at 95% confidence level on a combination of the parity-violating photon and electron coefficients kappa_{o+} and c. This new constraint provides an improvement over previous bounds by one order of magnitude.