Nonsingular Ekpyrotic Cosmology with a Nearly Scale-Invariant Spectrum of Cosmological Perturbations and Gravitational Waves

TL;DR

This paper introduces a string theory-inspired mechanism for a non-singular bounce in cosmology, producing nearly scale-invariant spectra of fluctuations and gravitational waves, with testable predictions for upcoming experiments.

Contribution

It presents a novel non-singular Ekpyrotic cosmology model that naturally generates scale-invariant spectra of perturbations and gravitational waves, differing from previous models.

Findings

Produces nearly scale-invariant scalar and tensor spectra.

Predicts equal scalar and tensor tilts.

Gravitational wave amplitude depends on string-to-Planck scale ratio.

Abstract

We propose a mechanism borrowed from string theory which yields a non-singular transition from a phase of Ekpyrotic contraction to the expanding phase of Standard Big Bang cosmology. The same mechanism converts the initial vacuum spectrum of cosmological fluctuations before the bounce into a scale-invariant one, and also changes the spectrum of gravitational waves into an almost scale-invariant one. The scalar and tensor tilts are predicted to be the same, in contrast to the predictions from the "String Gas Cosmology" scenario. The amplitude of the gravitational wave spectrum depends on the ratio of the string scale to the Planck scale and may be in reach of upcoming experiments.