Bulk inflaton shadows of vacuum gravity

TL;DR

This paper presents a higher-dimensional vacuum framework for analyzing bulk inflaton models with exponential potentials, simplifying the study of cosmological perturbations and connecting solutions to known gravity solutions.

Contribution

It introduces a $(5+m)$-dimensional vacuum approach to bulk inflaton models, enabling straightforward analysis of perturbations and linking solutions to pure gravity in higher dimensions.

Findings

Derived master equations for perturbations with simple boundary conditions.

Connected inflationary solutions to known higher-dimensional vacuum solutions.

Identified complexities in scalar perturbations with massive modes.

Abstract

We introduce a $(5+m)$-dimensional vacuum description of five-dimensional bulk inflaton models with exponential potentials that makes analysis of cosmological perturbations simple and transparent. We show that various solutions, including the power-law inflation model recently discovered by Koyama and Takahashi, are generated from known $(5+m)$-dimensional vacuum solutions of pure gravity. We derive master equations for all types of perturbations, and each of them becomes a second order differential equation for one master variable supplemented by simple boundary conditions on the brane. One exception is the case for massive modes of scalar perturbations. In this case, there are two independent degrees of freedom, and in general it is difficult to disentangle them into two separate sectors.