http://arxiv.org/abs/1910.01718
We implement adaptive mesh refinement (AMR) 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 $\mu \propto \ln{\lambda}$, defined by the string width parameter $\lambda$ over two orders of magnitude. We investigate the resulting massless (Goldstone boson or axion) radiation and massive (Higgs) radiation signals, using quantitative diagnostic tools and geometries to determine the eigenmode decomposition of these radiation components. 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 characterised by the inverse square of the amplitude being proportional to the inverse tension $\mu$ for $3\lesssim \lambda \lesssim 100$. We conclude that analytic radiation modelling in the thin-string (Nambu-Goto) limit provides the appropriate cosmological limit for global strings. We also make a preliminary study of massive radiation modes, including the large $\lambda$ regime in which they become strongly suppressed relative to the preferred massless channel. We comment on the implications of this study for predictions of axions and gravitational waves produced by cosmic string networks.
A. Drew and E. Shellard
Mon, 7 Oct 19
32/42
Comments: 26 pages, 34 figures
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