  Quantum phenomena such as vacuum polarisation in curved spacetime induce
interactions between photons and gravity with quite striking consequences,
including the violation of the strong equivalence principle and the apparent
prediction of `superluminal' photon propagation. These quantum interactions can
be encoded in an effective action. In this paper, we extend previous results on
the effective action for QED in curved spacetime due to Barvinsky, Vilkovisky
and others and present a new, local effective action valid to all orders in a
derivative expansion, as required for a full analysis of the quantum theory of
high-frequency photon propagation in gravitational fields.
