Particle creation in a tunneling universe

TL;DR

This paper investigates particle creation during universe tunneling, clarifying that previous claims of catastrophic production were due to initial state choices, using a superspace model with a conformally coupled scalar field.

Contribution

It demonstrates that proper initial state selection resolves the controversy over particle creation during tunneling in a closed universe with a cosmological constant.

Findings

No particle production in the conformally coupled massless scalar field case.

Previous claims of catastrophic particle production are due to initial state mischoices.

Breakdown of semiclassical approximation is linked to initial state selection.

Abstract

An expanding closed universe filled with radiation can either recollapse or tunnel to the regime of unbounded expansion, if the cosmological constant is nonzero. We re-examine the question of particle creation during tunneling, with the purpose of resolving a long-standing controversy. Using a perturbative superspace model with a conformally coupled massless scalar field, which is known to give no particle production, we explicitly show that the breakdown of the semiclassical approximation and the ``catastrophic particle production'' claimed earlier in the literature are due to an inappropriate choice of the initial quantum state prior to the tunneling.