Non-Gaussianities in New Ekpyrotic Cosmology

TL;DR

New Ekpyrotic Cosmology advocates a slow-contraction early universe with a ghost-condensate bounce and a second scalar field that sources entropy perturbations to imprint a scale-invariant curvature perturbation. The model includes a non-singular exit that preserves ζ through the bounce, leading to a consistent hot big-bang phase. It predicts large non-Gaussianities in the 3- and 4-point functions, with a local f_NL and substantial tau_NL and kappa_NL, offering a distinctive observational signature that can differentiate it from inflationary scenarios. These non-Gaussian predictions, including their specific shape-dependence, render Planck and near-future CMB experiments capable of testing the viability of this paradigm against slow-roll inflation and other alternatives.

Abstract

New Ekpyrotic Cosmology is an alternative scenario of the early universe which relies on a phase of slow contraction before the big bang. We calculate the 3-point and 4-point correlation functions of primordial density perturbations and find a generically large non-Gaussian signal, just below the current sensitivity level of CMB experiments. This is in contrast with slow-roll inflation, which predicts negligible non-Gaussianity. The model is also distinguishable from alternative inflationary scenarios that yield large non-Gaussianity, such as DBI inflation and the simplest curvaton-like models, through the shape dependence of the correlation functions. Non-Gaussianity therefore provides a distinguishing and testable prediction of New Ekpyrotic Cosmology.