Investigating Isocurvature Perturbations and non-Gaussianities in a Two-Field System with Generalised Kinetic Terms

The physics of the very early universe is well described by the inflationary paradigm, a period of accelerated expansion of the universe driven by vacuum energy. Quantum fluctuations give rise to curvature perturbations that act as the seed for large-scal e structure. One of the simplest models of inflation is a single scalar field, slowly rolling down its potential. The predictions of an almost scale invariant power spectrum (like that observed in the cosmic microwave background) that are obtained from mo dels of this type are encouraging but, with the increasing quality of data expected from the Planck satellite, many authors have sought alternative models, many with predictions of non-Gaussianity. The aim of this project is to find a general formalism wi th which to understand the properties of multi-field inflationary models such as DBI inflation, k-inflation as well as inflation driven by coupled scalar fields. The particular focus of the investigation will be the evolution of the curvature and isocurv ature fluctuations, and non-Gaussianity predictions. A theoretical description of this kind would be an invaluable tool to aid in the understanding of the properties of two-field inflation. The fellowship is sought to allow for two research visits to th e University of Oslo of five and four weeks' duration respectively. During this time progress on the theoretical side of the project would be greatly aided by working in collaboration with observational cosmologists at the University of Oslo on the proble m of non-Gaussianity. The interval between the research visits would allow for work to be done in collaboration with members of the Astroparticle and Cosmology group at the University of Sheffield. Slow-roll inflation is often considered to be a effectiv e theory and a thorough grasp of the issues in this area is essential to develop our understanding of the physics of the early universe.