Adiabatic Spectra During Slowly Evolving

TL;DR

This paper demonstrates that during slow expansion or contraction, the increasing mode of curvature perturbation can produce a scale-invariant spectrum consistent with observations, offering a new perspective on early universe models.

Contribution

It shows that the increasing mode during slow evolution phases can generate scale-invariant spectra, expanding the understanding of perturbation origins beyond constant modes.

Findings

Increasing mode can produce scale invariance during slow phases

Perturbations can naturally exit the horizon in this scenario

Amplitude matches observational data

Abstract

In general, for single field, the scale invariant spectrum of curvature perturbation can be given by either its constant mode or its increasing mode. We show that during slowly expanding or contracting, the spectrum of curvature perturbation given by its increasing mode can be scale invariance. The perturbation mode can be naturally extended out of horizon, and the amplitude of perturbation is consistent with the observations. We briefly discuss the implement of this scenario.