K-Bounce

TL;DR

This paper analyzes the conditions for nonsingular bounces in one-degree-of-freedom models, examining how perturbations behave and are transferred through the bounce, especially focusing on spectral distortions at different wavelengths.

Contribution

It narrows the class of viable bounce models by imposing nonsingularity and well-behaved perturbations, and characterizes the transfer matrix of perturbations during the bounce.

Findings

Spectral distortions occur mainly at small wavelengths.

Long wavelength perturbations pass through the bounce unaffected.

Nonsingular bounce models are constrained by perturbation behavior.

Abstract

By demanding that a bounce is nonsingular and that perturbations are well-behaved at all times, we narrow the scope of possible models with one degree of freedom that can describe a bounce in the absence of spatial curvature. We compute the general properties of the transfer matrix of perturbations through the bounce, and show that spectral distortions of the Bardeen potential $\Phi$ are generically produced only for the small wavelengths, although the spectrum of long wavelength curvature perturbations produced in a contracting phase gets propagated unaffected through such a bounce.