Numerical simulations of necklaces in SU(2) gauge-Higgs field theory

TL;DR

This paper presents the first numerical simulations of non-Abelian gauge theory necklaces, revealing their scaling behavior and monopole distribution, which impacts gravitational wave constraints on cosmic strings.

Contribution

It introduces the first numerical simulation of necklaces in a non-Abelian gauge theory, demonstrating their scaling behavior and monopole distribution in a cosmological context.

Findings

Necklaces exhibit scaling behavior similar to cosmic string networks.

The monopole-to-string energy density ratio decreases over time.

A large number of monopoles remain on strings, affecting loop dynamics.

Abstract

We perform the first numerical simulations of necklaces in a non-Abelian gauge theory. Necklaces are composite classical solutions which can be interpreted as monopoles trapped on strings, rather generic structures in a Grand Unified Theory. We generate necklaces from random initial conditions, modelling a phase transition in the early Universe, and study the evolution. For all cases, we find that the necklace system shows scaling behaviour similar to that of a network of ordinary cosmic strings. Furthermore, our simulations indicate that comoving distance between the monopoles or semipoles along the string asymptotes to a constant value at late times. This means that while the monopole-to-string energy density ratio decreases as the inverse of the scale factor, a horizon-size length of string has a large number of monopoles, significantly affecting the dynamics of string loops. We argue that gravitational wave bounds from millisecond pulsar timing on the string tension in the Nambu-Goto scenario are greatly relaxed.