A confirmation of agreement of different approaches for scalar gauge-invariant metric perturbations during inflation

TL;DR

This paper confirms that different methods for calculating gauge-invariant scalar metric perturbations during inflation yield consistent results, extending the formalism to large amplitude fluctuations in a single-field inflationary model.

Contribution

It demonstrates the agreement of various approaches for scalar gauge-invariant metric perturbations during inflation, including large amplitude fluctuations, within a single-field framework.

Findings

Different approaches agree on scalar perturbation spectra.

Formalism applies to large amplitude fluctuations.

Results are valid for cosmological scales where vector and tensor modes are negligible.

Abstract

We revisit an extension of the well-known formalism for gauge-invariant scalar metric fluctuations, to study the spectrums for both, the inflaton and gauge invariant (scalar) metric fluctuations in the framework of a single field inflationary model where the quasi-exponential expansion is driven by an inflation which is minimally coupled to gravity. The proposal here examined is valid also for fluctuations with large amplitude, but for cosmological scales, where vector and tensor perturbations can be neglected and the fluid is irrotacional.