The tunneling wavefunction in Kantowski-Sachs quantum cosmology

TL;DR

This paper investigates the tunneling wave function in Kantowski-Sachs quantum cosmology, revealing conditions for universe nucleation, anisotropy evolution, and the impact of additional terms on nucleation probability.

Contribution

It analyzes initial conditions for universe creation in Kantowski-Sachs models using path integrals, highlighting the importance of boundary conditions and topological considerations.

Findings

Acceptable initial condition is fixing the $S^1$ radius to zero with smooth closure.

The wave function predicts an initially anisotropic inflating universe that becomes isotropic.

Nucleation probability is not exponentially suppressed unless a Gauss-Bonnet term is included.

Abstract

We use a path-integral approach to study the tunneling wave function in quantum cosmology with spatial topology $S^{1}\times S^{2}$ and positive cosmological constant (the Kantowski-Sachs model). If the initial scale factors of both $S^1$ and $S^2$ are set equal to zero, the wave function describes (semiclassically) a universe originating at a singularity. This may be interpreted as indicating that an $S^1\times S^2$ universe cannot nucleate out of nothing in a non-singular way. Here we explore an alternative suggestion by Halliwell and Louko that creation from nothing corresponds in this model to setting the initial volume to zero. We find that the only acceptable version of this proposal is to fix the radius of $S^1$ to zero, supplementing this with the condition of smooth closure (absence of a conical singularity). The resulting wave function predicts an inflating universe of high anisotropy, which however becomes locally isotropic at late times. Unlike the de Sitter model, the total nucleation probability is not exponentially suppressed, unless a Gauss-Bonnet term is added to the action.