. cl as s - ph ] 1 8 O ct 2 00 5 1 A precision test of the isotropy of the speed of light using rotating cryogenic optical cavities

A test of Lorentz invariance for electromagnetic waves was performed by comparing the resonance frequencies of two stable optical resonators as a function of orientation in space. The crystalline resonators were operated at 3.4 K in a cryostat employing a pulse-tube refrigerator. A new analysis yields the Robertson-Mansouri-Sexl theory parameter combination β − δ − 1/2 = (−0.6 ± 2.1 ± 1.2) · 10 −10 and one parameter of the Standard Model Extension theory, (˜ κe−) ZZ = (−2.9 ± 2.2) · 10 −14. The isotropy of space is a well-tested symmetry of nature [1]. Because it is a foundation of today's accepted theories of the fundamental forces it continues to be the focus of both theoretical and experimental studies. A series of experiments [2, 3, 4] have recently been performed with the goal of improving the limits for a hypothetical violation. They were in part motivated by the development of an extension of the Standard Model (SME) by Kosteleck´y and coworkers [5, 6] that describes Lorentz violation in a comprehensive way. This dynamical test theory indicates that isotropy violation, if it exists, may exhibit characteristics that differ from those of previous kinematic test theories, such as the Robertson-Mansouri-Sexl (RMS) theory [7]. Here, we will not discuss the conceptual frameworks used to describe hypothetical violations of isotropy, since this is reported in the literature and is also treated in this Proceedings volume. In this contribution, we limit ourselves to the description of an experiment used to perform an improved test of the isotropy of the speed of light. The experiment has already been presented previously [8]; here we give a more detailed description and report an extension of the data analysis. The experiment was conceived as an actively rotated Michelson-Morley experiment using ultrastable optical cavities interrogated by lasers. It was a natural extension of our previous work with stationary resonators [3, 9], but employed a completely new apparatus, except for the sapphire optical cavities.