Abstract

The detection of gravitational waves by LIGO has opened up a new window into observational cosmology. This has encouraged research into gravitational wave signatures from other sources, such as cosmic strings and phase transitions in the early universe, as well as alternative dark matter candidates. In this talk, we present numerical investigations of global topological strings and their radiation pathways, which can be applied either to cosmic or dark matter axion strings. There has been debate in the literature over the dominant mechanisms for this radiation and the resulting spectrum, in part due to the approximations used, either idealised as one-dimensional Nambu-Goto strings or with the limited dynamic range of field theory simulations. We demonstrate how the application of the numerical technique of adaptive mesh refinement, using the public code GRChombo, yields new insights into string radiation and backreaction and may resolve this controversy. The direct analogy between massless Goldstone boson (or axion) radiation and gravitational radiation means that these methods should also enable accurate prediction of gravitational wave signatures.