Effective action for bubble nucleation rates

We develop a method to calculate the prefactor in the expression for the bubble nucleation rate. A fermion with Yukawa coupling is considered where a step potential can be used as a good approximation in the thin wall limit. Corrections due to thicker walls are investigated by perturbing about the thin wall case. We derive the thermal one loop effective action, calculating it numerically, and find that the prefactor in the nucleation rate can both suppress and enhance, for a given temperature, when the usual renormalisation conditions are applied to the effective potential. (C) 2002 Elsevier Science B.V. All rights reserved.