Hohensee, Michael A.Stanwix, PaulTobar, Michael E.Parker, Steven R.Phillips, David F.Walsworth, Ronald2012-12-062010Hohensee, Michael A., Paul L. Stanwix, Michael E. Tobar, Stephen R. Parker, David F. Phillips, and Ronald L. Walsworth. 2010. Improved constraints on isotropic shift and anisotropies of the speed of light using rotating cryogenic sapphire oscillators. Physical Review D 82(7): 076001.1550-23681550-7998http://nrs.harvard.edu/urn-3:HUL.InstRepos:10001144We 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 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 \(7.4 \times 10^{-9}\). 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 nonbirefringent terms in the photon sector of the minimal standard model extension.en-USatomic clocktimeJournal Article2012-12-0610.1103/PhysRevD.82.076001