Late-Time Coarsening of a Bistable Coherence Field in Expanding Cosmology: A Regime-Delimited Model Beyond the Boyanovsky–de Vega Large-N Domain

We study the late-time coarsening dynamics of a scalar coherence field C(x,t) ∈ [0,1] governed by a bistable Allen–Cahn / Wright–Fisher reaction–diffusion equation in a spatially flat FRW background. This work does not dispute the Boyanovsky–de Vega scaling result for symmetry breaking in FRW cosmologies; it identifies a distinct late-time dissipative regime in which the observables, assumptions, and effective dynamics differ from those of the large-N quantum-field calculation. Through determini