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

Quantum-gravity phenomenology, Lorentz symmetry, and the SME

Violations of spacetime symmetries have recently been identified as promising signatures for physics underlying the Standard Model. The present talk gives an overview over various topics in this field: The motivations for spacetime-symmetry research, including some mechanisms for Lorentz breaking, are reviewed. An effective field theory called the Standard-Model Extension (SME) for the description of the resulting low-energy effects is introduced, and some experimental tests of Lorentz and CPT invariance are listed.Comment: 8 pages, 2 figures, Plenary talk at 12th Mexican School on Particles and Fields and 6th Latin American Symposium on High Energy Physics (VI-Silafae/XII-MSPF), Puerto Vallarta, Mexico, 1-8 Nov 200

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