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University of Cambridge > Talks.cam > Theoretical Physics Colloquium > Causality and Microcausaliy in Curved Spacetime

## Causality and Microcausaliy in Curved SpacetimeAdd to your list(s) Download to your calendar using vCal - Graham Shore (Swansea)
- Wednesday 28 November 2007, 14:15-15:30
- MR2, Centre for Mathematical Sciences.
If you have a question about this talk, please contact Daniel Wesley. We consider how causality and micro-causality are realised in QED in curved spacetime. The photon propagator is found to exhibit novel non-analytic behaviour due to vacuum polarization, which invalidates the Kramers-Kronig dispersion relation and calls into question the validity of micro-causality in curved spacetime. This non-analyticity is ultimately related to the generic focusing nature of congruences of geodesics in curved spacetime, as implied by the null energy condition, and the existence of conjugate points. These results arise from a calculation of the complete non-perturbative frequency dependence of the vacuum polarization tensor in QED , using novel world-line path integral methods together with the Penrose plane-wave limit of spacetime in the neighbourhood of a null geodesic. The refractive index of curved spacetime is shown to exhibit superluminal phase velocities, dispersion, absorption (due to \gamma \to e This talk is part of the Theoretical Physics Colloquium series. ## This talk is included in these lists:- All CMS events
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