Physics of the Early Universe

Cosmology spans a wide range of physics, from the very small scales and high energies of the early Universe to the large scale dynamics of galaxies. This diversity is met with a corresponding array of techniques to study various phenomena, ranging from quantum gravity to classical dynamics and analytic calculations to numerical simulations. On the largest observable scales the Cosmic Microwave Background (CMB), relic radiation from the big bang, and the clustering of galaxies allow us to probe the expansion history and constituents of the Universe. These observations suggest that most of the Universe is composed of exotic dark matter and dark energy. Understanding the nature of these components, and connecting observations of the Universe with particle physics, is a major outstanding issue for cosmology and one of the goals of our work. The standard model of particle physics is extremely successful at describing the results from various sources, including collider experiments. It does however have some conceptual problems (for instance the existance of a large number of free parameters) which motivate the study of various extensions. We will use ideas from non-commutative geometry, which provides a natural framework for the symmetries of the standard model, to constrain the free parameters and make testable predictions. Another well motivated extension of the standard model is supersymmetry which postulates a symmetry between bosons and fermions. Supersymmetry leads to different dynamics at phase transitions and bubbles can nucleate. This may explain why there is more matter than anti-matter in the Universe and we will perform numerical simulations of this process. The standard model includes the strong nuclear force, which governs the behaviour of a quark-gluon plasma. This novel state of matter is currently being probed at colliders, however it is extremely complicated to describe using orthodox methods. There has recently been great interest in the possibility that techniques derived from string theory can be employed, and we will explore the physics of these plasmas using these insights. Particle physics and general relativity both break down at extreme energies, where a unified theory of quantum gravity is expected to operate. We will test the observational consequences of two such theories, string theory and non-metric gravity. String theory allows superstrings to stretch across the Universe, altering the fluctuations in the CMB, producing gravitational waves, emmitting high energy particles and lensing galaxies, while non-metric theories of gravity may successfully reproduce the rotation curves of galaxies as well as their lensing properties. Another feature of string theory is that it offers a new set of degrees of freedom called moduli fields. The behaviour of these fields will lead to potentially observable consequences which could provide observational evidence for, or undermine, string theory. We will calculate how the moduli behave as the Universe evolves and examine their relation to dark energy and dark matter.