Cosmology without inflation

TL;DR

This paper introduces a non-singular, geodesically complete cosmological model where the universe contracts before bouncing into expansion, offering new solutions to standard cosmological puzzles without relying on inflation.

Contribution

It presents a novel bouncing cosmology framework that is non-singular and horizon-free, with explicit models demonstrating scale-invariant spectra from a contracting phase.

Findings

The model is geodesically complete and avoids singularities.

Scale-invariant spectra can be generated during contraction.

Quantum effects can induce a bounce in a dust-dominated universe.

Abstract

We propose a new cosmological paradigm in which our observed expanding phase is originated from an initially large contracting Universe that subsequently experienced a bounce. This category of models, being geodesically complete, is non-singular and horizon-free, and can be made to prevent any relevant scale to ever have been smaller than the Planck length. In this scenario, one can find new ways to solve the standard cosmological puzzles. One can also obtain scale invariant spectra for both scalar and tensor perturbations: this will be the case, for instance, if the contracting Universe is dust-dominated at the time at which large wavelength perturbations get larger than the curvature scale. We present a particular example based on a dust fluid classically contracting model, where a bounce occurs due to quantum effects, in which these features are explicit.