Cosmological constraints on Lorentz violation in electrodynamics

Test of the isotropy of the speed of light using a continuously rotating optical resonator

We report on a test of Lorentz invariance performed by comparing the resonance frequencies of one stationary optical resonator and one continuously rotating on a precision air bearing turntable. Special attention is paid to the control of rotation induced systematic effects. Within the photon sector of the standard model extension, we obtain improved limits on combinations of 8 parameters at a level of a few parts in 10(-16). For the previously least well known parameter we find [EQUATION: SEE TEXT]. Within the Robertson-Mansouri-Sexl test theory, our measurement restricts the isotropy violation parameter [EQUATION: SEE TEXT]. corresponding to an eightfold improvement with respect to previous nonrotating measurements.

Modern Tests of Lorentz Invariance

Motivated by ideas about quantum gravity, a tremendous amount of effort over the past decade has gone into testing Lorentz invariance in various regimes. This review summarizes both the theoretical frameworks for tests of Lorentz invariance and experimental advances that have made new high precision tests possible. The current constraints on Lorentz violating effects from both terrestrial experiments and astrophysical observations are presented.

Test of Lorentz invariance in electrodynamics using rotating cryogenic sapphire microwave oscillators

We present the first results from a rotating Michelson-Morley experiment that uses two orthogonally orientated cryogenic sapphire resonator oscillators operating in whispering gallery modes near 10 GHz. The experiment is used to test for violations of Lorentz invariance in the framework of the photon sector of the standard model extension (SME), as well as the isotropy term of the Robertson-Mansouri-Sexl (RMS) framework. In the SME we set a new bound on the previously unmeasured kappa(ZZ)(e-) component of 2.1(5.7) x 10(-14), and set more stringent bounds by up to a factor of 7 on seven other components. In the RMS a more stringent bound of -0.9(2.0) x 10(-10) on the isotropy parameter, P(MM) = delta-beta + 1 / 2 is set, which is more than a factor of 7 improvement.

Bound on Lorentz and CPT violating boost effects for the neutron

A search for an annual variation of a daily sidereal modulation of the frequency difference between colocated 129Xe and 3He Zeeman masers sets a stringent limit on boost-dependent Lorentz and CPT violation involving the neutron, consistent with no effect at the level of 150 nHz. In the framework of the general standard-model extension, the present result provides the first clean test for the fermion sector of the symmetry of spacetime under boost transformations at a level of 10(-27) GeV.

Vacuum Cerenkov radiation

Within the classical Maxwell-Chern-Simons limit of the standard-model extension, the emission of light by uniformly moving charges is studied confirming the possibility of a Cerenkov-type effect. In this context, the exact radiation rate for charged magnetic point dipoles is determined and found in agreement with a phase-space estimate under certain assumptions.

New limits on Planck scale Lorentz violation in QED

Constraints on possible Lorentz symmetry violation (LV) of order E/M(Planck) for electrons and photons in the framework of effective field theory (EFT) are discussed. Using (i) the report of polarized MeV emission from GRB021206 and (ii) the absence of vacuum Cerenkov radiation from synchrotron electrons in the Crab Nebula, we improve previous bounds by 10(-10) and 10(-2), respectively. We also show that the LV parameters for positrons and electrons are different, discuss electron helicity decay, and investigate how prior constraints are modified by the relations between LV parameters implied by EFT.

Vacuum photon splitting in Lorentz-violating quantum electrodynamics

Radiative corrections arising from Lorentz violation in the fermion sector induce a nonzero amplitude for vacuum photon splitting. At one loop, the on-shell amplitude acquires both CPT-even and CPT-odd contributions forbidden in conventional electrodynamics.

New limit on signals of Lorentz violation in electrodynamics

We describe the results of an experiment to test for spacetime anisotropy terms that might exist from Lorentz violations. The apparatus consists of a pair of cylindrical superconducting cavity-stabilized oscillators operating in the TM010 mode with one axis east-west and the other vertical. Spatial anisotropy is detected by monitoring the beat frequency at the sidereal rate and its first harmonic. We see no anisotropy to a part in 10(13). This puts a comparable bound on four linear combinations of parameters in the general standard model extension, and a weaker bound of < 4 x 10(-9) on three others.

Observational bounds on quantum gravity signals using existing data

We consider a new set of effects arising from the quantum gravity corrections to the propagation of fields, associated with fluctuations of the spacetime geometry. Using already existing experimental data, we can put bounds on these effects that are more stringent by several orders of magnitude than those expected to be obtained in astrophysical observations. In fact, these results can already be interpreted as questioning the whole scenario of linear (in l(P)) corrections to the dispersion relations for free fields in Lorentz violating theories.

Clock-comparison tests of Lorentz and CPT symmetry in space

Clock-comparison experiments conducted in space can provide access to many unmeasured coefficients for Lorentz and CPT violation. The orbital configuration of a satellite platform and the relatively large velocities attainable in a deep-space mission would permit a broad range of tests with Planck-scale sensitivity.