New Ekpyrotic Cosmology
Evgeny I. Buchbinder, Justin Khoury, Burt A. Ovrut

TL;DR
This paper introduces a new ekpyrotic cosmology model with a non-singular bounce, generating a scale-invariant spectrum of density fluctuations consistent with observations, as an alternative to inflation.
Contribution
It presents a novel ekpyrotic scenario combining ghost condensate to achieve a non-singular bounce and produce observable density perturbations.
Findings
Achieves a non-singular bounce without ghost instabilities.
Produces a nearly scale-invariant curvature perturbation spectrum.
Predicts negligible gravitational waves on observable scales.
Abstract
In this paper, we present a new scenario of the early Universe that contains a pre big bang Ekpyrotic phase. By combining this with a ghost condensate, the theory explicitly violates the null energy condition without developing any ghost-like instabilities. Thus the contracting universe goes through a non-singular bounce and evolves smoothly into the expanding post big bang phase. The curvature perturbation acquires a scale-invariant spectrum well before the bounce in this scenario. It is sourced by the scale-invariant entropy perturbation engendered by two ekpyrotic scalar fields, a mechanism recently proposed by Lehners et al. Since the background geometry is non-singular at all times, the curvature perturbation remains nearly constant on super horizon scales. It emerges from the bounce unscathed and imprints a scale-invariant spectrum of density fluctuations in the matter-radiation…
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