Couplings varying on cosmological scales and Lorentz breaking

Abstract

In the context of N=4 supergravity in four dimensions, we present an exact classical solution that leads to spacetime-dependent electromagnetic couplings and discuss the ensuing Lorentz-violating effects. We comment briefly on experimental bounds.

Comments: 10 pages, 1 figure, invited talk presented at the Coral Gables Meeting, December 2002