On the four-dimensional effective theories in brane-worlds

TL;DR

This paper explores four-dimensional effective theories derived from higher-dimensional brane-world models, analyzing their observational implications, especially in the context of inflation and non-Gaussianities.

Contribution

It develops a systematic approach to derive 4D effective theories from various higher-dimensional brane-world models using the gradient expansion method.

Findings

Derived 4D effective gravity theories for multiple higher-dimensional models.

Analyzed observational consequences of these theories in brane-world inflation.

Investigated non-Gaussianities in inflationary models within this framework.

Abstract

Models with extra dimensions have attracted much interest recently because they may provide the solution for long standing problems in physics. One interesting and very attractive idea is that our visible universe is confined to a four-dimensional hypersurface in a higher-dimensional spacetime. This membrane like universe was dubbed brane-world. The main goal of this thesis is the study of the four-dimensional (4D) effective theories and their observational consequences in the brane-world universe. After introducing the brane-world idea with some detail we shall use the gradient expansion method to obtain the 4D effective theories of gravity for several higher-dimensional theories with different numbers of extra-dimensions. In the second half of the thesis, after introducing the concept of brane-inflation we will focus on some observational consequences of these low energy effective theories. In particular, the last two chapters before the conclusion are devoted to the study of non-Gaussianities in general models of inflation.