Tests of Lorentz invariance using a microwave resonator: an update

The frequencies of a cryogenic sapphire oscillator and a hydrogen maser are compared to set new constraints on a possible violation of Lorentz invariance. We determine the variation of the oscillator frequency as a function of its orientation (Michelson-Morley test) and of its velocity (Kennedy-Thorndike test) with respect to a preferred frame candidate. We constrain the corresponding parameters of the Mansouri and Sexl test theory to /spl delta/-/spl beta/+ 1/2 /spl les/3.4/spl times/10/sup -9/ and /spl beta/-/spl alpha/-1/spl les/4.1/spl times/10/sup -7/ which is of the same order as the best previous result for the former and represents a 50 fold improvement for the latter. These results correspond to an improvement of our previously published limits by about a factor 2. We describe the changes of the experiment, and show the new data that lead to that improvement.