Scale invariant scalar metric fluctuations during inflation: non-perturbative formalism from a 5D vacuum

TL;DR

This paper develops a 5D non-perturbative formalism to analyze scalar metric fluctuations during inflation, revealing that the spectrum can be scale invariant with sub-Planckian inflaton values, differing from 4D results.

Contribution

It introduces a 5D approach to inflationary fluctuations, showing potential scale invariance and sub-Planckian inflaton values, extending previous 4D models.

Findings

Spectrum of fluctuations can be scale invariant in 5D

Inflaton field can be sub-Planckian during inflation

Differences from 4D formalism in fluctuation spectrum

Abstract

We extend to 5D an approach of a 4D non-perturbative formalism to study scalar metric fluctuations of a 5D Riemann-flat de Sitter background metric. In contrast with the results obtained in 4D, the spectrum of cosmological scalar metric fluctuations during inflation can be scale invariant and the background inflaton field can take sub-Planckian values.