PHOTON AND GRAVITON GREEN-FUNCTIONS ON COSMIC STRING SPACE-TIMES

We present the Green's functions for photons and gravitons in the vicinity of an idealized cosmic string. We stress the importance of the Ward identities involved and the necessity for "smoothing" the curvature singularity in the space-time in order to carry out the calculations. The Green's functions are employed to determine the renormalized vacuum expectation value of the stress-energy tensor for scalar, electromagnetic, and linearized gravitational fields propagating in the neighborhood of an idealized cosmic string.