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CATEGORIES:Theoretical Physics Colloquium
SUMMARY:Causality and Microcausaliy in Curved Spacetime -
Graham Shore (Swansea)
DTSTART;TZID=Europe/London:20071128T141500
DTEND;TZID=Europe/London:20071128T153000
UID:TALK8082AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/8082
DESCRIPTION:We consider how causality and micro-causality are
realised in QED in curved spacetime. The photon pr
opagator is found to exhibit novel non-analytic be
haviour due to vacuum polarization\, which invalid
ates the Kramers-Kronig dispersion relation and ca
lls into question the validity of micro-causality
in curved spacetime. This non-analyticity is ultim
ately related to the generic focusing nature of co
ngruences of geodesics in curved spacetime\, as im
plied by the null energy condition\, and the exist
ence of conjugate points. These results arise from
a calculation of the complete non-perturbative fr
equency dependence of the vacuum polarization tens
or in QED\, using novel world-line path integral m
ethods together with the Penrose plane-wave limit
of spacetime in the neighbourhood of a null geodes
ic. The refractive index of curved spacetime is sh
own to exhibit superluminal phase velocities\, dis
persion\, absorption (due to \\gamma \\to e^+e^-)
and bi-refringence\, but we demonstrate that the w
avefront velocity (the high-frequency limit of the
phase velocity) is indeed c\, thereby guaranteein
g that causality itself is respected.
LOCATION:MR2\, Centre for Mathematical Sciences
CONTACT:Daniel Wesley
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