Bremsstrahlung and Pair Creation by a Photon in the Spacetime of a Cosmic String

Abstract

We consider two tree-graph processes in the spacetime of an infinite, straight and static cosmic string, namely Bremsstrahlung and electron–positron pair production. Results based on a simplified model with scalar fields which were obtained by other authors are extended to the more realistic QED case. In empty Minkowski spacetime, energy and momentum conservation preclude these processes. In spite of the local flatness of the metric, it is a topological defect that gives rise to non-conservation of momentum in the plane perpendicular to the string. Analytic expressions for the total transition probabilities and, in the case of Bremsstrahlung, the total radiation energy are found and compared with the results for the scalar field model. In a sense, the cylindrical mode solutions of the Dirac equation allow a spatial localisation of the decay processes relative to the string axis.