Precision test of the isotropy of light propagation

We report on a test of the isotropy of light propagation performed by comparing the resonance frequencies of two orthogonal cryogenic optical resonators subject to Earth's rotation over similar to1 yr. The technical aspects of the experiment are discussed and the analysis of the data is presented in detail. For a possible anisotropy of the speed of light c, we obtain Delta(theta)c/c(0)=(2.6+/-1.7)x10(-15). Within the general extension of the standard model of particle physics, we extract limits on seven parameters at accuracies down to 10(-15), improving the best previous result by about two orders of magnitude. Within the Robertson-Mansouri-Sexl test theory, this implies an isotropy-violation parameter beta-delta-1/2=(2.2+/-1.5)x10(-9), about three times lower than the best previous result.