Topics in Cosmology

TL;DR

This paper reviews inflationary cosmology, explores the theory of cosmological perturbations, discusses conceptual issues in early universe models, and introduces string gas cosmology as an alternative structure formation mechanism without inflation.

Contribution

It introduces string gas cosmology as a novel paradigm for early universe structure formation, challenging the inflationary model.

Findings

String gas cosmology offers a potential alternative to inflation.

The model provides a mechanism for structure formation without inflation.

Conceptual problems in current paradigms are addressed.

Abstract

These lectures present a brief review of inflationary cosmology, provide an overview of the theory of cosmological perturbations, and then focus on the conceptual problems of the current paradigm of early universe cosmology, thus motivating an exploration of the potential of string theory to provide a new paradigm. Specifically, the string gas cosmology model is introduced, and a resulting mechanism for structure formation which does not require a period of cosmological inflation is discussed.