Couplings varying on cosmological scales and Lorentz breaking

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.Comment: 10 pages, 1 figure, invited talk presented at the Coral Gables Meeting, December 200

Cosmology and spacetime symmetries

Cosmological models often contain scalar fields, which can acquire global nonzero expectation values that change with the comoving time. Among the possible consequences of these scalar-field backgrounds, an accelerated cosmological expansion, varying couplings, and spacetime-symmetry violations have recently received considerable attention. This talk studies the interplay of these three key signatures of cosmologically varying scalars within a supergravity framework.Comment: 5 pages; Prepared for New Worlds in Astroparticle Physics, Faro, Portugal, January 8-10, 200

Apparent Lorentz violation through spacetime-varying couplings

In this talk, we explore the relation between smoothly varying couplings and Lorentz violation. Within the context of a supergravity model, we present an explicit mechanism that causes the effective fine-structure parameter and the effective electromagnetic $\theta$ angle to acquire related spacetime dependences. We argue that this leads to potentially observable Lorentz violation and discuss some implications for the Standard-Model Extension.Comment: 8 pages; Presented at the 4th Meeting on New Worlds in Astroparticle Physic