Cobordism and Bubbles of Anything in the String Landscape

TL;DR

This paper develops a 4D effective field theory framework to analyze bubble decay and creation processes in string theory models, predicting the existence of end-of-the-world branes via the Cobordism Conjecture.

Contribution

It introduces a novel 4D EFT description of ETW branes in string compactifications, generalizing bubble solutions and enabling rate calculations for vacuum transitions.

Findings

Established a formalism for decay and creation rates of bubbles of anything.

Connected ETW branes with the Cobordism Conjecture predictions.

Provided explicit constructions for type IIB Calabi-Yau orientifolds.

Abstract

We study bubble of nothing decays and their reverse processes, the creation of vacua through `bubbles of something', in models of the Universe based on string theory. From the four-dimensional perspective, the corresponding gravitational instantons contain an end-of-the-world (ETW) boundary or brane, realized by the internal manifold shrinking to zero size. The existence of such ETW branes is predicted by the Cobordism Conjecture. We develop the 4d EFT description of such boundaries at three levels: First, by generalizing the Witten bubble through an additional defect. Second, by replacing the compact $S^1$ with a Calabi-Yau orientifold and allowing it to shrink and disappear through a postulated defect. Third, we describe an ETW brane construction for type IIB Calabi-Yau orientifold compactifications with O3/O7 planes through an appropriate additional O5 orientifolding. Our 4d EFT formalism allows us to compute the decay/creation rates for bubbles of anything depending on two parameters: The size of the relevant defect and its tension a.k.a. the induced (generalized) deficit angle.