Dynamics of metastable vacua in the early universe

We study the question whether a possible metastable vacuum state is actuall y populated in a phase transition in the early universe, as is usually assu med in the discussion of vacuum stability bounds e.g. for Standard Model pa rameters. A phenomenological (3 + 1)-dimensional Langevin equation is solve d numerically for a toy model with a potential motivated by the finite temp erature 1-loop effective potential of the Standard Model including addition al non-renormalizable operators from an effective theory for physics beyond the Standard Model and a time dependent temperature. It turns out that whe ther the metastable vacuum is populated depends critically on the value of the phenomenological parameter eta for small scalar couplings. For large en ough scaler couplings and with our specific form of the non-renormalizable operators the system (governed by the Langevin equation) always ends up in the metastable minimum. (C) 1999 Published by Elsevier Science B.V. All rig hts reserved.