Revisiting Metastable Cosmic String Breaking

TL;DR

This paper reevaluates the decay rate of metastable cosmic strings by considering their finite size, providing a more reliable lower limit on the tunneling factor, which is relevant for interpreting recent gravitational wave signals.

Contribution

It introduces a finite-size analysis of cosmic string decay, improving upon the traditional thin-string approximation and offering robust lower bounds on decay rates.

Findings

Finite size effects significantly alter decay rate estimates.

A robust lower limit on the tunneling factor is established.

Implications for gravitational wave signals from cosmic strings.

Abstract

Metastable cosmic strings appear in models of new physics with a two-step symmetry breaking $G\to H\to 1$, where $\pi_1(H)\neq 0$ and $\pi_1(G)=0$. They decay via the monopole-antimonopole pair creation inside. Conventionally, the breaking rate has been estimated by an infinitely thin string approximation, which requires a large hierarchy between the symmetry breaking scales. In this paper, we reexamine it by taking into account the finite sizes of both the cosmic string and the monopole. We obtain a robust lower limit on the tunneling factor $e^{-S_B}$ even for regimes the conventional estimate is unreliable. In particular, it is relevant to the cosmic string interpretation of the gravitational wave signals recently reported by pulsar timing array experiments.