Testing Nambu-Goto approximation of cosmic string by lattice field simulations

TL;DR

This study compares gravitational wave spectra from cosmic string networks using lattice field simulations and the Nambu-Goto approximation, finding good agreement for near-global strings and highlighting the dominance of particle emission over gravitational waves.

Contribution

It provides a detailed numerical comparison between lattice field simulations and the Nambu-Goto approximation for cosmic strings, clarifying their validity across different gauge couplings.

Findings

Discrepancy between NG and lattice simulations is negligible for near-global strings.

Discrepancy increases with gauge coupling in local strings.

Particle emission dominates energy loss, with GW to particle energy ratio of 10^{-3} to 10^{-2}.

Abstract

The precise calculation of gravitational wave (GW) and particle emissions from cosmic string networks is of significant theoretical and experimental interest. In this Letter, we perform numerical simulations of near-global and local string networks, comparing the GW spectra predictions from both lattice field simulation and the Nambu-Goto (NG) approximation methods. We find the discrepancy between the GW spectra computed via the NG approximation and the lattice field simulation is negligible for near-global string and grow with increasing gauge coupling. Additionally, we confirm that particle emission significantly dominates energy emission, with the ratio of GW energy to particle energy approximately $10^{-3}$ to $10^{-2}$ for both near-global and local string scenarios.