Slow-roll approximation in quantum cosmology

TL;DR

This paper provides a detailed analysis of complex solutions in quantum cosmology with slow-roll scalar fields, refining previous results and applying a complexified slow-roll approximation to both Hartle-Hawking and Vilenkin wave functions.

Contribution

It introduces a complexified slow-roll approximation method to analyze $O(4)$-symmetric solutions, sharpening classical results and applying to both wave functions in quantum cosmology.

Findings

Refined the classical regime analysis of no-boundary wave function.

Applied complexified slow-roll approximation to both Hartle-Hawking and Vilenkin wave functions.

Predicted a family of inflationary universes with different weights.

Abstract

In minimally coupled scalar field theories with a potential of the slow-roll type, we give a detailed description of the complex $O(4)$-symmetric solutions to Einstein's equations on the four-ball which contribute to the no-boundary amplitude $\Psi_\textsf{NB}(b,\chi)$ for a closed universe to contain a round three-sphere spatial slice of size $b$ covered homogeneously with the scalar field at value $\chi$. Our derivation demonstrates a result anticipated by Hartle, Hawking and Hertog in Phys. Rev. D 77 (2008) 123537 [arXiv:0803.1663], sharpens Vilenkin's result in Phys. Rev. D 37 (1988) 888 in the classical regime of the minisuperspace and makes use of a complexified slow-roll approximation. Our technique applies to both the Hartle-Hawking and Vilenkin wave functions, which both predict a family of inflationary universes but weight each member exponentially differently in the semiclassical approximation.