THERMAL PHASE MIXING DURING FIRST-ORDER PHASE-TRANSITIONS

The dynamics of first-order phase transitions are studied in the context of (3+1)-dimensional scalar field theories. Particular attention is paid to the question of quantifying the strength of the transition, and how "weak" and "strong" transitions have different dynamics. We propose a model with two available low temperature phases separated by an energy barrier so that one of them becomes metastable below the critical temperature Tc. The system is initially prepared in this phase and is coupled to a thermal bath. Investigating the system at its critical temperature we find that "strong" transitions are characterized by the system remaining localized within its initial phase, while "weak" transitions are characterized by considerable phase mixing. Always at Tc, we argue that the two regimes are themselves separated by a (second-order) phase transition, with order parameter given by the equilibrium fractional population difference between the two phases and control parameter given by the strength of the scalar field's quartic self-coupling constant. We obtain a Ginzburg-like criterion to distinguish between "weak" and "strong" transitions, in agreement with previous results in 2+1 dimensions. © 1995 The American Physical Society.