Vacuum decay in multidimensional field landscapes: thin, thick and intersecting walls

TL;DR

This paper investigates vacuum decay in multidimensional fields, revealing new eigenvalues in instantons and discussing how bubble wall interactions influence decay rates and stability.

Contribution

It introduces the effect of additional vacua on instanton eigenvalues and explores how finite wall thickness regulates potential decay rate enhancements.

Findings

New vanishing eigenvalue in instanton fluctuation determinant

Finite wall thickness regulates decay rate enhancement

Existence of novel saddle points affecting vacuum stability

Abstract

We study tunneling between vacua in multi-dimensional field spaces. Working in the strict thin wall approximation, we find that the conventional instantons for false vacuum decay develop a new vanishing eigenvalue in their fluctuation determinant, arising from decorations of the nucleating bubble wall with small spots of the additional vacua. Naively, this would suggest that the presence of additional vacua in field space leads to a substantial enhancement of the nucleation rate. However, we argue that this potential enhancement is regulated away by the finite thickness of physical bubble wall intersections. We then discuss novel saddle points of the thin wall action that, in some regimes of parameter space, have the potential to destabilize the conventional instantons for false vacuum decay.