Radiation from global topological strings using adaptive mesh refinement: Methodology and massless modes

Abstract

We implement adaptive mesh refinement simulations of global topological strings using the public numerical relativity code, GRChombo. We perform a quantitative investigation of the dynamics of single sinusoidally displaced string configurations, studying a wide range of string energy densities $\ensuremath{\mu}\ensuremath{\propto}\mathrm{ln}\ensuremath{\lambda}$, defined by the string width parameter $\ensuremath{\lambda}$ over 2 orders of magnitude. We investigate the resulting massless (Goldstone boson or axion) radiation signals, using quantitative diagnostic tools to determine the eigenmode decomposition. Given analytic radiation predictions, we compare the oscillating string trajectory with a backreaction model accounting for radiation energy losses, finding excellent agreement. We establish that backreaction decay is accurately characterized by the inverse square of the amplitude being proportional to the inverse tension $\ensuremath{\mu}$ for $3\ensuremath{\lesssim}\ensuremath{\lambda}\ensuremath{\lesssim}100$. We conclude that analytic radiation modeling in the thin-string (Nambu-Goto) limit provides the appropriate cosmological limit for global strings. We contextualize these results with respect to axions and gravitational waves produced by cosmic string networks.

Topics & Concepts