I've Got the World on a Brane

TL;DR

This thesis explores advanced models of extra dimensions involving branes, including their reduction, singularity behavior, and multi-galileon theories, with implications for phenomenology and cosmology.

Contribution

It provides a five-dimensional reduction of Heterotic M-Theory valid to all orders and develops new multi-galileon braneworld models with codimension greater than one.

Findings

The reduced theory offers a new framework for phenomenological studies.

Singularity analysis suggests a big crunch rather than a black brane.

Constructed multi-galileon models extend braneworld theory.

Abstract

This thesis treats several topics in the study of extra-dimensional models of the world, concerning Heterotic M-Theory and the dynamics of branes. We describe a reduction to five dimensions, over a Calabi-Yau manifold, of an improved version of Heterotic M-Theory, which is valid to all orders in the gravitational coupling. This provides a starting point for considering the consequences of the improved theory for the very fruitful phenomenology of the original. We investigate the singularities formed by the collision of gravitating branes in scalar field theory. By considering the asymptotic structure of the spacetime, the properties of the horizons formed and the growth of the curvature we argue that the singularity is not a black brane, as one might have expected, but rather a big crunch. Finally, we construct a restricted class of multi-galileon theories as braneworld models with codimension greater than one, developing in the process some of the formalism needed for the general construction.