PhD Thesis: String theory in the early universe

Abstract

The intersection of string theory with cosmology is unavoidable in the early universe, and its exploration may shine light on both fields. In this thesis, three papers at this intersection are presented and reviewed, with the aim of providing a thorough and pedagogical guide to their results. First, we address the longstanding problem of finding a string theory realisation of the axion. Using warped compactifications in heterotic string theory, we show that the axion decay constant can be lowered to acceptable values by the warp factor. Next, we move to the subject of cosmic strings, whose network evolution could have important consequences for astrophysics and cosmology. In particular, there are quantitative differences between cosmic superstring networks and GUT cosmic string networks. We investigate the properties of cosmic superstring networks in warped backgrounds, giving the tension and properties of three-string junctions in these backgrounds. Finally, we examine the possibility that cosmic strings in heterotic string theory could be responsible for generating the galactic magnetic fields that seeded those observed today.

152 pages, 17 figures, 2 tables. PhD thesis

References in corpus (31)

• Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• An Improved Experimental Limit on the Electric Dipole Moment of the Neutron
• The Anthropic Landscape of String Theory
• A Mini-Landscape of Exact MSSM Spectra in Heterotic Orbifolds
• The Heterotic Road to the MSSM with R parity
• Fitting CMB data with cosmic strings and inflation
• Heterotic GUT and Standard Model Vacua from simply connected Calabi-Yau Manifolds
• Status of Oscillation plus Decay of Atmospheric and Long-Baseline Neutrinos
• Gravitational Waves from Broken Cosmic Strings: The Bursts and the Beads
• Comparing Infrared Dirac-Born-Infeld Brane Inflation to Observations
• Constraints on string networks with junctions
• Axion Inflation and Gravity Waves in String Theory
• The (p,q) String Tension in a Warped Deformed Conifold
• Introduction to Cosmic F- and D-Strings
• Cosmic strings reborn?
• A Model of Anthropic Reasoning, Addressing the Dark to Ordinary Matter Coincidence
• Bulk antisymmetric tensor fields in a Randall-Sundrum model
• Conifolds and Geometric Transitions
• Cosmic Necklaces from String Theory
• Modification of Decay Constants of Superstring Axions: Effects of Flux Compactification and Axion Mixing
• Lumps in the throat
• Non-Abelian (p,q) Strings in the Warped Deformed Conifold
• Lensing and CMB Anisotropies by Cosmic Strings at a Junction
• Hubble Imaging Excludes Cosmic String Lens
• Magnetogenesis from Cosmic String Loops
• Dipole-Deformed Bound States and Heterotic Kodaira Surfaces
• Energy Radiation by Cosmic Superstrings in Brane Inflation
• New Limits on Gravitational Radiation using Pulsars
• Coherence Constraint on the Existence of Cosmic Defects
• Axion as a CDM component
• Neutrino Masses and Mixing - Theory