University of Cambridge > Talks.cam > DAMTP Friday GR Seminar > Radiation from Global Cosmic Strings with Adaptive Mesh Refinement

Radiation from Global Cosmic Strings with Adaptive Mesh Refinement

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Cosmic strings are a well-motivated potential source both of dark matter axions and gravitational waves, arising naturally from spontaneous symmetry breaking in field theories. Although they are modelled usefully by the Nambu-Goto action, their complex non-linear dynamics introduces uncertainties which can have a significant effect on their predicted radiative spectra. We present adaptive mesh refinement (AMR) simulations of global cosmic strings using the public numerical relativity code, GRChombo, to evolve the underlying complex field equations, to address this issue. We perform a quantitative investigation of the dynamics of single sinusoidally displaced string configurations, studying a wide range of string energy densities μ∝lnλ, defined by the string width parameter λ over two orders of magnitude. We investigate the resulting massless (Goldstone boson or axion) and massive radiation signals, using quantitative diagnostic tools to determine the eigenmode decomposition and compare the oscillating string trajectory with an inverse square backreaction model accounting for radiation energy losses, finding excellent agreement. We further find that non-linear massive radiation is (exponentially) suppressed with increasing λ. We conclude that analytic radiation modelling in the thin-string (Nambu-Goto) limit provides the appropriate cosmological limit for global strings. We comment on the implications of this study for predictions of axions and gravitational waves produced by cosmic string networks, as well as preliminary work towards implementing global string evolution in full numerical relativity.

This talk is part of the DAMTP Friday GR Seminar series.

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