Cosmological Fluctuations from Infra-Red Cascading During Inflation

TL;DR

This paper introduces a new mechanism during inflation where infra-red cascading of scalar fields generates non-Gaussian cosmological fluctuations, potentially dominating over standard fluctuations and creating observable features.

Contribution

The paper presents a novel IR cascading mechanism during inflation, showing how particle production leads to distinctive non-Gaussian curvature fluctuations with a bump-shaped spectrum.

Findings

IR cascading generates a bump in the curvature fluctuation spectrum.

The resulting fluctuations are significantly non-Gaussian.

The effect can dominate over standard inflationary fluctuations for certain parameters.

Abstract

We propose a qualitatively new mechanism for generating cosmological fluctuations from inflation. The non-equilibrium excitation of interacting scalar fields often evolves into infra-red (IR) and ultra-violet (UV) cascading, resulting in an intermediate scaling regime. We observe elements of this phenomenon in a simple model with inflaton \phi and iso-inflaton \chi fields interacting during inflation via the coupling g^2 (\phi-\phi_0)^2 \chi^2. Iso-inflaton particles are created during inflation when they become instantaneously massless at \phi=\phi_0, with occupation numbers not exceeding unity. We point out that very quickly the produced \chi particles become heavy and their multiple re-scatterings off the homogeneous condensate \phi(t) generates bremschtrahlung radiation of light inflaton IR fluctuations with high occupation numbers. The subsequent evolution of these IR fluctuations is qualitatively similar to that of the usual inflationary fluctuations, but their initial amplitude is different. The IR cascading generates a bump-shaped contribution to the cosmological curvature fluctuations, which can even dominate over the usual fluctuations for g^2>0.06. The IR cascading curvature fluctuations are significantly non-gaussian and the strength and location of the bump are model-dependent, through g^2 and \phi_0. The effect from IR cascading fluctuations is significantly larger than that from the momentary slowing-down of \phi(t). With a sequence of such bursts of particle production, the superposition of the bumps can lead to a new broad band non-gaussian component of cosmological fluctuations added to the usual fluctuations. Such a sequence of particle creation events can, but need not, lead to trapped inflation.