Improved Constraints on Isotropic Shift and Anisotropies of the Speed of Light using Rotating Cryogenic Sapphire Oscillators

TL;DR

This paper uses rotating cryogenic sapphire oscillators to set new, highly precise limits on isotropic and anisotropic deviations in the speed of light, improving constraints on fundamental physics parameters.

Contribution

It introduces a novel analysis method for Michelson-Morley experiments to simultaneously constrain all non-birefringent SME photon sector parameters.

Findings

First Michelson-Morley experiment constraint on 

Achieved a constraint on  of 7.4 10^{-9}

First analysis of a single experiment to limit all nine non-birefringent SME photon sector terms

Abstract

We demonstrate that Michelson-Morley tests, which detect direction-dependent anisotropies in the speed of light, can also be used to place limits upon isotropic deviations of the vacuum speed of light from $c$, as described by the photon sector Standard Model Extension (SME) parameter $\tilde{\kappa}_{tr}$. A shift in the speed of light that is isotropic in one inertial frame implies anisotropic shifts in others. Using observer Lorentz covariance, we derive the time-dependent variations in the relative resonance frequencies of a pair of electromagnetic resonators that would be generated by such a shift in the rest frame of the Sun. A new analysis of a recent experimental test of relativity using this result constrains $\tilde{\kappa}_{tr}$ with a precision of $7.4\times10^{-9}$. This represents the first constraint on $\tilde{\kappa}_{tr}$ by a Michelson-Morley experiment and the first analysis of a single experiment to simultaneously set limits on all nine non-birefringent terms in the photon sector of the SME.