Kavli Affiliate: E. P. S. Shellard
| First 5 Authors: Amelia Drew, E. P. S. Shellard, , ,
| Summary:
We implement adaptive mesh refinement (AMR) simulations of global topological
strings using the public code, GRChombo. We perform a quantitative
investigation of massive radiation from single sinusoidally displaced string
configurations, studying a range of string widths defined by the coupling
parameter $lambda$ over two orders of magnitude, effectively varying the mass
of radiated particles $m_H sim sqrt{lambda}$. We perform an in-depth
investigation into the effects of AMR on massive radiation emission, including
radiation trapping and the refinement required to resolve high frequency modes.
We use quantitative diagnostic tools to determine the eigenmode decomposition,
showing a complex superposition of high frequency propagating modes with
different phase and group velocities. We conclude that massive radiation is
generally strongly suppressed relative to the preferred massless channel, with
suppression increasing at lower amplitudes and higher $lambda$. Only in
extreme nonlinear regimes (e.g. with relative amplitude $varepsilon sim 1.5$
and $lambda < 1$) do we observe massive and massless radiation to be emitted
at comparable magnitude. We find that massive radiation is emitted in distinct
high harmonics of the fundamental frequency of the string, and we demonstrate
that, for the sinusoidal configurations studied, massive radiation is
exponentially suppressed with $sqrt{lambda}$ (i.e. the particle mass).
Finally, we place these results in the context of axions and gravitational
waves produced by cosmological cosmic string networks, and note that AMR
provides a significant opportunity to explore higher $lambda$ (thin string)
regimes whilst using fewer computational resources.
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