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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 yr. For a possible anisotropy of the speed of light c, we obtain _c/c₀= (2. 61. 7) 10^-15. Within the Robertson-Mansouri-Sexl (RMS) test theory, this implies an isotropy violation parameter --12= (-2. 21. 5) 10^-9, about 3 times lower than the best previous result. 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 2 orders of magnitude.
Müller et al. (2003) studied this question.