Nucleation at finite temperature beyond the superminispace model

TL;DR

This paper investigates the quantum-to-classical transition in universe nucleation beyond simplified models, deriving criteria for transition types and analyzing phase diagrams for scalar and vector fields.

Contribution

It introduces a perturbation expansion approach around the sphaleron configuration to analyze nucleation transitions beyond the superminispace model.

Findings

Scalar fields exhibit both first and second order transitions depending on potential shape.

Vector field transition is exclusively first order.

A phase diagram for scalar and vector fields is established.

Abstract

The transition from the quantum to the classical regime of the nucleation of the closed Robertson-Walker Universe with spacially homogeneous matter fields is investigated with a perturbation expansion around the sphaleron configuration. A criterion is derived for the occurrence of a first-order type transition, and the related phase diagram for scalar and vector fields is obtained. For scalar fields both the first and second order transitions can occur depending on the shape of the potential barrier. For a vector field, here that of an O(3) nonlinear $\sigma$-model, the transition is seen to be only of the first order.