Gravitational wave and particle emission from a cosmic string loop: local case

TL;DR

This study uses lattice simulations to analyze how local cosmic string loops emit particles and gravitational waves, revealing that particle emission dominates in realistic network loops, significantly suppressing the expected gravitational wave background.

Contribution

It provides the first detailed comparison of particle and gravitational wave emission from local string loops using lattice simulations, highlighting the dominance of particle emission in realistic scenarios.

Findings

Particle emission dominates in network loops with realistic length-to-core ratios.

Gravitational wave emission is more significant in artificial, smaller loops.

The gravitational wave background from local strings is likely much weaker than previously estimated.

Abstract

Using lattice field simulations of the Abelian-Higgs model, we characterize the simultaneous emission of (scalar and gauge) particles and gravitational waves (GWs) by local string loops. We use {\it network} loops created in a phase transition, and {\it artificial} loops formed by either crossing straight-boosted or curved-static infinite strings. Loops decay via both particle and GW emission, on time scales $\Delta t_{\rm dec} \propto L^p$, where $L$ is the loop length. For particle production, we find $p \simeq 2$ for artificial loops and $p \simeq 1$ for network loops, whilst for GW emission, we find $p \simeq 1$ for all loops. We find that below a critical length, artificial loops decay primarily through particle production, whilst for larger loops GW emission dominates. However, for network loops, which represent more realistic configurations, particle emission always dominates, as supported by our data with length-to-core ratios up to $L/r_\text{c} \lesssim 6000$. Our results indicate that the GW background from a local string network should be greatly suppressed compared to estimations that ignore particle emission.