Black holes as bubble nucleation sites

TL;DR

This work investigates how inhomogeneities, modeled as a seed black hole in a Schwarzschild–de Sitter background, catalyze false vacuum decay by constructing Euclidean singular instantons with conical deficits. The authors compute the on-shell Euclidean action, show the action reduces to a horizon-area sum independent of the Euclidean time period, and demonstrate that bubble nucleation is significantly enhanced relative to Coleman–de Luccia, with a critical seed mass M_C separating regimes with or without a remnant black hole inside the bubble. They connect these Euclidean results to a Lorentzian WKB picture of bubble-to-bubble transitions, revealing a crossing relation between spontaneous nucleation and transitions dependent on black-hole entropy. The findings imply that black holes can act as efficient nucleation sites for true-vacuum bubbles, potentially altering cosmological evolution of metastable vacua and motivating further exploration in higher dimensions and alternative compactifications.

Abstract

We consider the effect of inhomogeneities on the rate of false vacuum decay. Modelling the inhomogeneity by a black hole, we construct explicit Euclidean instantons which describe the nucleation of a bubble of true vacuum centred on the inhomogeneity. We find that inhomogeneity significantly enhances the nucleation rate over that of the Coleman-de Luccia instanton -- the black hole acts as a nucleation site for the bubble. The effect is larger than previously believed due to the contributions to the action from conical singularities. For a sufficiently low initial mass, the original black hole is replaced by flat space during this process, as viewed by a single causal patch observer. Increasing the initial mass, we find a critical value above which a black hole remnant survives the process. This resulting black hole can have a higher mass than the original black hole, but always has a lower entropy. We compare the process to bubble-to-bubble transitions, where there is a semi-classical Lorentzian description in the WKB approximation.