Influence of Super-Horizon Scales on Cosmological Observables Generated during Inflation

TL;DR

This paper investigates how super-horizon scale fluctuations during inflation influence observable cosmological perturbations, revealing scale-dependent imprints, a blue tilt in the power spectrum, and enhanced non-Gaussianity, consistent with recent CMB observations.

Contribution

It introduces a novel out-of-equilibrium field theory approach to analyze super-horizon effects on inflationary perturbations, highlighting memory effects and scale-dependent signatures.

Findings

Super-horizon fluctuations leave measurable imprints on observable scales.

A blue tilt of the power spectrum is found on large scales.

Enhanced non-Gaussianity is predicted on large scales.

Abstract

Using the techniques of out-of-equilibrium field theory, we study the influence on the properties of cosmological perturbations generated during inflation on observable scales coming from fluctuations corresponding today to scales much bigger than the present Hubble radius. We write the effective action for the coarse-grained inflaton perturbations integrating out the sub-horizon modes, which manifest themselves as a colored noise and lead to memory effects. Using the simple model of a scalar field with cubic self-interactions evolving in a fixed de Sitter background, we evaluate the two- and three-point correlation function on observable scales. Our basic procedure shows that perturbations do preserve some memory of the super-horizon-scale dynamics, in the form of scale-dependent imprints in the statistical moments. In particular, we find a blue tilt of the power-spectrum on large scales, in agreement with the recent results of the WMAP collaboration which show a suppression of the lower multipoles in the Cosmic Microwave Background anisotropies, and a substantial enhancement of the intrinsic non-Gaussianity on large scales