Pre-inflationary perturbations spectrum

TL;DR

This paper derives a model of inflation where the scalar field evolves linearly on a plateau, showing that certain perturbation spectra remain nearly unchanged through the inflationary phase.

Contribution

It introduces a specific inflationary regime with a linearly evolving scalar field and analyzes the preservation of perturbation spectra during inflation.

Findings

Perturbation spectra are conserved across the inflationary phase.

The model aligns with the slow-rolling approximation.

Inhomogeneous scales near the horizon are preserved after inflation.

Abstract

In the framework of a flat FLRW model we derive an inflationary regime in which the scalar field, laying on the plateau of its potential, admits a linear time dependence and remains close to a constant value. The behaviour of inhomogeneous perturbations is determined on the background metric in agreement to the "slow-rolling" approximation. We show that the inhomogeneous scales which before inflation were not much greater then the physical horizon, conserve their spectrum (almost) unaltered after the de Sitter phase.