Understanding the accelerated expansion of the Universe

Amazing progress has been made in the study of the universe over the last twenty years, leading many to say that we live in a "golden age of cosmology". Observations of the cosmic microwave background (CMB), photons that have been moving freely for most of the age of the universe, have been revolutionised by satellite observations and are continuing to improve. The pattern of temperature perturbations of CMB photons contain hidden signatures of the Big Bang that are now being revealed.
However the initial source of the CMB perturbations is remains unknown. A brief period of exponential expansion, called inflation, solves several cosmological problems such as why the universe looks the same in every direction, even though there wasn't time for the early universe (without inflation) to reach thermal equilibrium. Quantum fluctuations are inflated as well and may become the initial seeds of all perturbations. So inflation links the very smallest (quantum) and largest (galactic) scales. Today, the Universe is undergoing a second phase of accelerated expansion driven by dark energy, which is just a label given a component of the Universe which we do not understand. The aim of this project is to learn more about the physics behind inflation and dark energy.
Today we have precision era measurements of the cosmic microwave background and information about clusters of galaxies. These precision measurements are restricted to about 3 orders of magnitude in length scales. However, another 20-30 orders of magnitude in length scales must have also been produced by inflation on smaller scales. Therefore we know very little about the vast majority of the length scales on which quantum mechanical perturbations were produced during inflation. This limits our ability to learn about the physics of the early universe, for example, many models of inflation are still an excellent match to all of the observational data.
Philippa Cole will study models of the early universe - specifically inflation and reheating after inflation - using analytical and sometimes numerical techniques. For example, she will calculate the abundance of primordial black holes, ultra-compact mini haloes and gravitational waves produced by classes of inflationary models in which the amplitude of perturbations grow on small scales. Probing the small scales provides access to 20 decades (factor of ten differences) in length scales, which open a new window on the end of inflation and reheating. These scales contain completely new and potentially far more information which could revolutionise our understanding of inflation and the thermal history of the early universe. The study of reheating should reflect on recent developments in particle physics, especially the discovery of the Higgs, which is the first scalar field to be detected.