Metastable cosmic strings

TL;DR

Metastable cosmic strings, arising from certain GUT symmetry breaking patterns, decay via monopole nucleation and produce distinctive gravitational wave signals that could be detected by current and future observatories, offering insights into high-energy physics.

Contribution

This paper reviews the current understanding of metastable cosmic strings, their GUT embeddings, and their gravitational wave signatures, highlighting their potential detectability and implications for fundamental physics.

Findings

Metastable cosmic strings emit a suppressed low-frequency GW signal.

GW signals from these strings could be detected by LIGO, LISA, and pulsar timing arrays.

The GW spectrum can provide insights into GUT-scale physics.

Abstract

Many symmetry breaking patterns in grand unified theories (GUTs) give rise to cosmic strings that eventually decay when pairs of GUT monopoles spontaneously nucleate along the string cores. These strings are known as metastable cosmic strings and have intriguing implications for particle physics and cosmology. In this article, we discuss the current status of metastable cosmic strings, with a focus on possible GUT embeddings and connections to inflation, neutrinos, and gravitational waves (GWs). The GW signal emitted by a network of metastable cosmic strings in the early universe differs, in particular, from the signal emitted by topologically stable strings by a suppression at low frequencies. Therefore, if the underlying symmetry breaking scale is close to the GUT scale, the resulting GW spectrum can be accessible at current ground-based interferometers as well as at future space-based interferometers, such as LISA, and at the same time account for the signal in the most recent pulsar timing data sets. Metastable cosmic strings thus nourish the hope that future GW observations might shed light on fundamental physics close to the GUT scale.