Metastable strings at PTAs: classical stability analysis

TL;DR

This paper analyzes the classical stability of metastable strings from a specific symmetry breaking chain, crucial for understanding their decay and implications for gravitational wave signals detected by PTAs.

Contribution

It identifies parameter regions where these strings are classically stable or unstable, informing their potential decay channels and impact on gravitational wave observations.

Findings

Classical instabilities affect the parameter space relevant for PTAs.

Stable and unstable regions of the string network are mapped.

Implications for the fate of string networks are discussed.

Abstract

Metastable strings can arise from a two-step symmetry breaking chain of the type $SU(2) \to U(1) \to 1$.They can decay through quantum tunneling by nucleating a monopole-antimonopole pair, and are prominent candidates for explaining the gravitational wave background detected at Pulsar Timing Arrays (PTAs).We investigate the classical stability of the strings arising in this commonly-considered setup, which serves as a fundamental input for discussing their possible decay channels. We identify the regions of parameter space in which the strings are either classically stable or unstable. Our results show that classical instabilities can impact the parameter space relevant for PTAs. We also discuss the possible fate of the string network in the regions of classical instability.