Multifield effects in string cosmology

Observational cosmology will make great strides over the coming decade. Ground-based experiments will observe the polarisation of the Cosmic Microwave Background (CMB) with exceptional accuracy, and new satellite missions will map out the large-scale distribution of matter in the universe (LSS) to an unprecedented depth and precision. The CMB polarisation and the matter distribution both carry imprints of the primordial, very high-energy physics governing the early universe. Hence, these experiments provide rare, new opportunities to learn about fundamental theory from cosmology. Unfortunately, for several of the phenomenological parameters that experiments will constrain, the theoretically expected values or distributions are not known. This significantly limits the scientific impact of these large observational efforts, and may even lead to significant discoveries passing unnoticed. The goal of this project is to address this issue: by developing new tools for studying multiple-field systems in the low-energy limits of string compactifications and in field theory, this project will provide novel methods for computing the relevant cosmological observables from interesting extensions of particle physics at high energies. These techniques will for the first time allow for a systematic approach to multiple-field inflation and reheating in string theory, and will significantly extend the state-of-the-art in those fields. The results will provide robust targets for cosmological experiments, and will provide a framework in which new observational data from the next generation of CMB and LSS experiments can be interpreted.