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

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 European Synchrotron Radiation Facility's GRAAL facility constrains such anisotropies representing the first nonthreshold collision-kinematics study of Lorentz violation. When interpreted within the minimal standard-model extension, this result yields the two-sided limit of 1.6x10{sup -14} at 95% confidence level on a combination of the parity-violating photon and electron coefficients ({kappa}-tilde{sub o+}){sup YZ}, ({kappa}-tilde{sub o+}){sup ZX}, c{sub TX}, and c{sub TY}. This new constraint provides an improvement over previous bounds by 1 order of magnitude.