Numerical simulation of domain wall and first-order phase transition in an expanding universe

We numerically study the domain walls (DWs) dynamic through 3D lattice simulation, and show that DWs formed by the breaking of a discrete symmetry in the early Universe can be dissipated by a later cosmic first-order phase transition (PT), even if the DWs have entered the scaling regime. The decay speed of the DWs is characterized by the bubble nucleation rate of the first-order PT. The produced gravitational wave (GW) spectrum can be dominated by the first-order PT and is of a different shape in comparison to that of the DWs. The mechanism can be probed by the current and upcoming GW detectors.