A smooth bouncing cosmology with scale invariant spectrum

TL;DR

This paper introduces a smooth bouncing cosmology model that generates a nearly scale-invariant spectrum of perturbations, serving as an alternative to inflation with specific predictions on spectral tilt and non-Gaussianities.

Contribution

It presents a novel bouncing cosmology model that remains stable and valid within 4d effective field theory, producing observable predictions distinct from inflation.

Findings

Generates a nearly scale-invariant spectrum during contraction

Predicts a slightly blue spectral index, n_S >~ 1

Indicates no observable gravitational waves and high non-Gaussianities

Abstract

We present a bouncing cosmology which evolves from the contracting to the expanding phase in a smooth way, without developing instabilities or pathologies and remaining in the regime of validity of 4d effective field theory. A nearly scale invariant spectrum of perturbations is generated during the contracting phase by an isocurvature scalar with a negative exponential potential and then converted to adiabatic. The model predicts a slightly blue spectrum, n_S >~ 1, no observable gravitational waves and a high (but model dependent) level of non-Gaussianities with local shape. The model represents an explicit and predictive alternative to inflation, although, at present, it is clearly less compelling.