Limits on Light-Speed Anisotropies from Compton Scattering of High-Energy Electrons

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 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 $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ at 95% confidence level on a combination of the parity-violating photon and electron coefficients $({\stackrel{\texttildelow{}}{\ensuremath{\kappa}}}_{o+}{)}^{YZ}$, $({\stackrel{\texttildelow{}}{\ensuremath{\kappa}}}_{o+}{)}^{ZX}$, ${c}_{TX}$, and ${c}_{TY}$. This new constraint provides an improvement over previous bounds by 1 order of magnitude.