This paper reports numerical simulations of a simplified model of Grand Unified Theory (GUT) symmetry breaking. The authors find that the phase transition can produce two kinds of topological defects at once: domain walls (two-dimensional sheets that separate regions of different field values) and magnetic monopoles (point-like objects that carry magnetic charge). When both defects are present, they interact in several unexpected ways, including monopoles getting absorbed by walls, monopoles being produced when walls collapse, and the possibility that collapsing, magnetically charged walls could form magnetically charged black holes if gravity is included.

To make the problem tractable they did not simulate a full SU(5) GUT. Instead they used an SU(3) gauge theory with an adjoint scalar field that shares the same qualitative defect types. The scalar potential they used includes a small bias term (an ϵ term) that slightly favors some vacua over others. They set thermal initial conditions, cooled the system below the critical temperature to trigger symmetry breaking, and then evolved the classical field equations numerically. The paper gives the parameter choices used in the runs (for example gauge coupling g = 0.5, mass-squared m^2 = 0.5, quartic coupling λ = 0.75, and higher-order couplings λ6 = 1.0 and d6 = −5.9) and finds a vacuum expectation value η ≈ 1.13 for these choices. A damping term controlled by a parameter γ was included to model energy loss to other degrees of freedom.

In plain terms, domain walls form where the field picks different discrete vacua on either side. The small bias makes one vacuum slightly lower in energy, so the walls are unstable and eventually collapse. Monopoles are stable field configurations tied to the topology of the vacuum manifold; in this model they appear because the symmetry breaking leaves a nontrivial second homotopy group. As walls sweep through space they can capture monopoles and so reduce the number of free monopoles — a variant of the so-called sweeping mechanism that has been proposed to address the cosmological monopole problem.