Mode solutions to the wave equation on a rotating cosmic string background

A static rotating cosmic string metric is singular along a timelike line and fails to be globally hyperbolic; these features make it difficult to solve the wave equation by conventional energy methods. Working on a single angular mode at a time, we use microlocal methods to construct forward parametrices for wave and Klein--Gordon equations on such backgrounds.
Comment: 15 pages; improvements to exposition in response to referee comments