Gauge-invariant metric fluctuations from NKK theory of gravity: de Sitter expansion

TL;DR

This paper investigates gauge-invariant metric fluctuations within a Noncompact Kaluza-Klein gravity framework during de Sitter expansion, showing consistency with standard inflation results and highlighting the influence of the fifth coordinate on the fluctuation spectrum.

Contribution

It introduces a gauge-invariant analysis of metric fluctuations in NKK gravity during inflation, connecting higher-dimensional effects with standard 4D results.

Findings

Reproduces the standard density fluctuation relation $rac{\delta ho}{ ho} \\simeq 2\Phi$

Shows the fluctuation spectrum depends on the fifth coordinate

Demonstrates compatibility of NKK theory with inflationary perturbation results

Abstract

In this paper we study gauge-invariant metric fluctuations from a Noncompact Kaluza-Klein (NKK) theory of gravity in a de Sitter expansion. We recover the well known result $\delta\rho/\rho \simeq 2\Phi$, obtained from the standard 4D semiclassical approach to inflation. The spectrum for these fluctuations should be dependent of the fifth (spatial-like) coordinate.