# A review of gravitational waves from cosmic domain walls

## TL;DR

This paper reviews how unstable cosmic domain walls in the early universe can produce detectable gravitational waves, discussing constraints, predictions, and future observational prospects.

## Contribution

It provides a comprehensive review of gravitational wave signals from unstable domain walls, including cosmological constraints and implications for particle physics models.

## Key findings

- Current pulsar timing arrays partially exclude some parameter space.
- Next-generation gravitational wave detectors will explore wider parameter space.
- Estimates of gravitational wave amplitude and frequency from domain walls are provided.

## Abstract

In this contribution, we discuss the cosmological scenario where unstable domain walls are formed in the early universe and their late-time annihilation produces a significant amount of gravitational waves. After describing cosmological constraints on long-lived domain walls, we estimate the typical amplitude and frequency of gravitational waves observed today. We also review possible extensions of the standard model of particle physics that predict the formation of unstable domain walls and can be probed by observation of relic gravitational waves. It is shown that recent results of pulser timing arrays and direct detection experiments partially exclude the relevant parameter space, and that a much wider parameter space can be covered by the next generation of gravitational wave observatories.