ar X iv : h ep - p h / 01 11 02 6 v 1 2 N ov 2 00 1 Cosmological Constraints on Lorentz Violation in Electrodynamics

Lorentz violation is a promising candidate signal for Planck-scale physics [1]. For instance, it could arise in string theory [2] and is a basic feature of noncommutative field theories [3]. In quantum field theory at attainable energies, small violations can be incorporated into the standard model to yield a general Lorentzviolating standard-model extension [4]. Its lagrangian consists of all possible observer Lorentz scalars formed from standard-model fields while allowing for coupling coefficients with Lorentz indices. All renormalizable and gauge invariant terms relevant at low energies are explicitly known. The standard-model extension predicts definite experimental signals. In the fermion sector of the theory, various experiments have bounded coefficients for Lorentz violation. However, relatively little is known experimentally about the implications of the standard-model extension for the properties of light. In particular, no bounds have been placed on the CPT-even coefficients for Lorentz violation in the photon sector. In this work, we study these terms and use spectropolarimetry of cosmological sources to obtain stringent bounds on Lorentz violation comparable to the best current limits in the fermion sector. Extracted from the standard-model extension, the Lorentz-violating electrodynamics can be written in terms of the usual field strength Fμν ≡ ∂μAν − ∂νAμ, which incorporates the electric field ~ E and the magnetic field ~ B. The relevant lagrangian terms are [4,5]