Quantum propagation across cosmological singularities

Steffen Gielen, Neil Turok

Research output: Contribution to journalArticlepeer-review

Abstract

The initial singularity is the most troubling feature of the standard cosmology, which quantum effects are hoped to resolve. In this paper, we study quantum cosmology with conformal (Weyl) invariant matter. We show it is natural to extend the scale factor to negative values, allowing a large, collapsing Universe to evolve across a quantum "bounce" into an expanding Universe like ours. We compute the Feynman propagator for Friedmann-Robertson-Walker backgrounds exactly, identifying curious pathologies in the case of curved (open or closed) universes. We then include anisotropies, fixing the operator ordering of the quantum Hamiltonian by imposing covariance under field redefinitions and again finding exact solutions. We show how complex classical solutions allow one to circumvent the singularity while maintaining the validity of the semiclassical approximation. The simplest isotropic universes sit on a critical boundary, beyond which there is qualitatively different behavior, with potential for instability. Additional scalars improve the theory's stability. Finally, we study the semiclassical propagation of inhomogeneous perturbations about the flat, isotropic case, at linear and nonlinear order, showing that, at least at this level, there is no particle production across the bounce. These results form the basis for a promising new approach to quantum cosmology and the resolution of the big bang singularity.
Original languageEnglish
Article number103510
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Volume95
Issue number10
DOIs
Publication statusPublished - 18 May 2017

Keywords

  • gr-qc
  • astro-ph.CO
  • hep-th

Fingerprint

Dive into the research topics of 'Quantum propagation across cosmological singularities'. Together they form a unique fingerprint.

Cite this