# Barnacles and Gravity

## TL;DR

This paper extends the analysis of barnacle instantons, which mediate bubble wall decay in multivacuum theories, to include gravitational effects, revealing conditions where barnacles dominate vacuum decay.

## Contribution

It introduces gravitational effects into the study of barnacle instantons, expanding understanding of their role in vacuum decay processes.

## Key findings

- Barnacles can be the preferred decay mode in certain parameter regions.
- Gravity can enlarge the parameter space where barnacles dominate.
- The study connects barnacles to other heterogeneous decay scenarios.

## Abstract

Theories with more than one vacuum allow quantum transitions between them, which may proceed via bubble nucleation; theories with more than two vacua posses additional decay modes in which the wall of a bubble may further decay. The instantons which mediate such a process have $O(3)$ symmetry (in four dimensions, rather than the usual $O(4)$ symmetry of homogeneous vacuum decay), and have been called `barnacles'; previously they have been studied in flat space, in the thin wall limit, and this paper extends the analysis to include gravity. It is found that there are regions of parameter space in which, given an initial bubble, barnacles are the favoured subsequent decay process, and that the inclusion of gravity can enlarge this region. The relation to other heterogeneous vacuum decay scenarios, as well as some of the phenomenological implications of barnacles are briefly discussed.