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In the context of N=4 supergravity in four dimensions, we present an exactclassical solution that leads to spacetime-dependent electromagnetic couplingsand discuss the ensuing Lorentz-violating effects. We comment briefly onexperimental bounds.Comment: 10 pages, 1 figure, invited talk presented at the Coral Gables  Meeting, December 200

Couplings varying on cosmological scales and Lorentz breaking