Slow-roll approximation in quantum cosmology

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 ${\Psi }_{\text{NB}}(b,\chi )$ 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.

32+8 pages, 2 figures. Version to be published in Classical and Quantum Gravity

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