Nonsingular bouncing cosmology from general relativity: Scalar metric perturbations

TL;DR

This paper develops equations for scalar metric perturbations in a nonsingular bouncing cosmology within general relativity, revealing potential observational effects from a spacetime defect replacing the big bang singularity.

Contribution

It derives the perturbation equations in a nonsingular bounce model with a degenerate metric, introducing new effects like information transfer across the bounce.

Findings

Scalar perturbation solutions match conformal coordinate approach.

Linear perturbations may leave imprints from the spacetime defect.

New effects include across-bounce information transfer.

Abstract

We derive the equations of motion for scalar metric perturbations in a particular nonsingular bouncing cosmology, where the big bang singularity is replaced by a spacetime defect with a degenerate metric. The adiabatic perturbation solution is obtained for nonrelativistic hydrodynamic matter. We get the same result by working with conformal coordinates. This last method is also valid for vector and tensor metric perturbations, and selected results are presented. We, finally, discuss several new effects from the linear perturbations of this nonsingular bouncing cosmology, such as across-bounce information transfer and the possible imprint on cosmological perturbations from a new phase responsible for the effective spacetime defect.