The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the European Synchrotron Radiation Facility's GRAAL facility constrains such anisotropies representing the first nonthreshold collision-kinematics study of Lorentz violation. When interpreted within the minimal standard-model extension, this result yields the two-sided limit of 1.6×10(-14) at 95% confidence level on a combination of the parity-violating photon and electron coefficients (κ(o+))(YZ), (κ(o+))(ZX), c(TX), and c(TY). This new constraint provides an improvement over previous bounds by 1 order of magnitude.

We have studied the angular fluctuations in the speed of light with respect to the apex of the dipole of Cosmic Microwave Background (CMB) radiation using the experimental data obtained with GRAAL facility, located at the European Synchrotron Radiation Facility (ESRF) in Grenoble. The measurements were based on the stability of the Compton edge of laser photons scattered on the 6 GeV monochromatic electron beam. The results enable one to obtain a conservative constraint on the anisotropy in the light speed variations Δc(θ)/c<3×10-12, i.e. with higher precision than from previous experiments.

The recent precise Cosmic Microwave Background Radiation (CMB) measurements by COBE and other facilities can provide interesting possibilities for the experimental checking of some basic physical parameters. In this context the inverse Compton scattering of highly monochromatic and parallel electron beams on laser photons is proposed for testing special relativity and related basic principles. For CEBAF and SLC parameters, for example, one can expect a precision for the isotropy of the speed of light dc(θ)/c ≈ 10−13 – 10−14 and an upper limit for the hypothetical fundamental length λf ≃ 10−22 – 10−23 cm. In particular, of special interest can be the checking of the isotropy of the speed of light with respect the direction of the CMB dipole (a kind of Michelson-Morley experiment relative to the absolute "rest" coordinate system).

No abstract

No abstract