Exact and Perturbed Friedmann-Lemaitre Cosmologies

TL;DR

This thesis applies the 1+3 covariant approach to analyze both exact and perturbed Friedmann-Lemaitre cosmologies with multiple fluids, focusing on their behavior in realistic universe models with matter, radiation, and cosmological constant.

Contribution

It provides a detailed analysis of n-fluid FL models and their perturbations using the covariant formalism, offering insights into their physical behavior and stability.

Findings

Analysis of n-fluid FL cosmologies with multiple non-interacting fluids.

Behavior of scalar, vector, and tensor perturbations in dust and radiation backgrounds.

Insights into the evolution of cosmological perturbations with a cosmological constant.

Abstract

In this thesis we first apply the 1+3 covariant description of general relativity to analyze n-fluid Friedmann-Lemaitre (FL) cosmologies; that is, homogeneous and isotropic cosmologies whose matter-energy content consists of n non-interacting fluids. We are motivated to study FL models of this type as observations suggest the physical universe is closely described by a FL model with a matter content consisting of radiation, dust and a cosmological constant. Secondly, we use the 1+3 covariant description to analyse scalar, vector and tensor perturbations of FL cosmologies containing a perfect fluid and a cosmological constant. In particular, we provide a thorough discussion of the behaviour of perturbations in the physically interesting cases of a dust or radiation background.