Search for light-speed anisotropies using Compton scattering of high-energy electrons

Based on the high sensitivity of Compton scatteringoff ultra relativistic electrons, the possibility of anisotropies in the speedof lightis investigated. The result discussed in this contribution is based on the -ray beam of the ESRF’s GRAAL facility (Grenoble, France) and the search for siderealvariations in the energy of the Compton-edgephotons. The absence of oscillations yields the two- sided limitof 1.6 × 10 14 at 95 % confidence level on a combination of photon and electron coefficients of the minimal Standard Model Extension(mSME). This new constraint provides an improvement over previous bounds by one order of magnitude.