Effect of the domain wall network annihilation phase on the gravitational-wave spectrum

Determine how, and to what extent, the annihilation (collapse) phase of a cosmological domain wall network modifies the gravitational-wave spectrum emitted by the network, specifying the changes in spectral shape relative to the scaling-regime signal.

Background

Domain wall networks formed after discrete symmetry breaking enter a scaling regime and emit a stochastic background of gravitational waves. To avoid cosmological overclosure, a small explicit symmetry-breaking bias eventually induces collapse and annihilation of the network.

Recent numerical studies of gravitational-wave production during this annihilation phase report conflicting results: some find no deviation from the conventional subhorizon scaling behavior, while others observe a less steep ultraviolet slope or even a doubly broken power-law spectrum. This lack of consensus indicates that the impact of the collapse dynamics on the gravitational-wave spectrum is not yet established.