Tunnelling with Bianchi IX Instantons

TL;DR

This paper investigates Bianchi IX gravitational instantons, including regular and singular solutions, to understand initial universe conditions and the role of symmetry in Euclidean action, with implications for cosmological tunnelling.

Contribution

It extends the analysis of gravitational instantons to Bianchi IX models, examining both regular and singular solutions and their Euclidean actions in the context of universe initial conditions.

Findings

Higher symmetry instantons have lower Euclidean action.

Singular instantons can have divergent Euclidean action for simple potentials.

Symmetry considerations explain the finiteness of Hawking Turok instanton action.

Abstract

Within the context of finding the initial conditions of the universe we consider gravitational instantons falling into the Bianchi IX classification. That is, a Euclidean four-manifold with a metric that satisfies Einstein's equations with an induced metric on S^3 submanifolds that is homogeneous but anisotropic. As well as finding regular solutions to the field equations with a tunnelling scalar field, we also look at the case of singular instantons with a view to applying the results to generic potentials. The study is in agreement with the prejudice that instantons with higher symmetry have a lower Euclidean action, even when we consider the singular class of solutions. It is also found that the Euclidean action can diverge for simple potentials, showing that the Hawking Turok instanton had finite action owing to its symmetry.