We report on a new test of Lorentz invariance performed by comparing the resonance frequencies of two orthogonal cryogenic optical resonators subject to Earth's rotation over 1 year. For a possible anisotropy of the speed of light c, we obtain 2.6 +/- 1.7 parts in 10^15. Within the Robertson-Mansouri-Sexl test theory, this implies an isotropy violation parameter beta - delta - 1/2 of -2.2 +/- 1.5 parts in 10^9, about three times lower than the best previous result. Within the general extension of the standard model of particle physics, we extract limits on 7 parameters at accuracies down to a part in 10^15, improving the best previous result by about two orders of magnitude.
@article{arxiv.physics/0305117,
title = {Modern Michelson-Morley experiment using cryogenic optical resonators},
author = {Holger Mueller and Sven Herrmann and Claus Braxmaier and Stephan Schiller and Achim Peters},
journal= {arXiv preprint arXiv:physics/0305117},
year = {2008}
}