Nucleation of vacuum phase transitions by topological defects

TL;DR

This paper demonstrates that topological defects like monopoles and cosmic strings can serve as effective nucleation sites, lowering the Euclidean action and facilitating vacuum phase transitions in the early universe.

Contribution

It provides a calculation of the Euclidean action in the thin-wall approximation showing topological defects catalyze vacuum decay.

Findings

Topological defects reduce the Euclidean action for bubble nucleation.

Defects act as effective nucleation sites for vacuum transitions.

The analysis applies to both monopoles and cosmic strings.

Abstract

The Euclidean action is calculated in the thin-wall approximation for a first-order vacuum phase transition in which the bubble appears symmetrically around either a global monopole or a gauge cosmic string. The bubble is assumed to be much larger than the core size of the monopole or string. In both cases the value of the Euclidean action is shown to be reduced below the $O(4)$ symmetric action value, indicating that the topological defects act as effective nucleation sites for vacuum decay.