Tunneling with negative tension

TL;DR

This paper introduces a new class of thin-wall instantons with negative tension that can cause rapid tunneling between vacua, revealing potential non-perturbative instabilities in theories supporting such solutions.

Contribution

It presents two novel constructions of negative tension instantons in stable theories, expanding understanding of vacuum decay and non-perturbative effects in quantum gravity.

Findings

Negative tension instantons can dominate tunneling processes.

Spectral flow ensures causality for these instantons.

These solutions relate to bubble of nothing and string theory orientifolds.

Abstract

We describe a new family of thin-wall instantons, with negative tension bubble walls, that mediate tunneling between Minkowski or de Sitter vacua. Some of these instantons can have exponentially enhanced tunneling rates, and would dominate the Euclidean path integral, representing a severe non-perturbative instability in any theory which supports them. We give two constructions of these instantons in theories which are perturbatively stable, but violate the null energy condition. One construction uses a scalar field theory with higher-derivative kinetic term, and is similar to the Coleman-de Luccia positive tension instanton. The other construction employs a negative-tension boundary arising from Z_2 orbifolding: it resembles a "bubble of nothing" which nucleates and grows, consuming the surrounding de Sitter or Minkowski spacetime. We explain how the spectral flow for fluctutations about the thin-wall tunneling solutions automatically protects causality, for both positive and negative tension instantons. We comment briefly on the relation of these solutions to a Kalzua-Klein "bubble of nothing," cosmological models relying on ghost condensates, and string theory orientifolds.