Primordial Cosmology

Coordinators: Christopher Hirata, Eva Silverstein, Matias Zaldarriaga

Scientific Advisors: Dick Bond

Current and near-future observations of the CMB and large scale structure promise to significantly constrain the mechanisms behind the primordial fluctuations responsible for structure formation in the observed universe. There is mounting evidence that the flatness of the universe and its structure derive from a primordial epoch of inflation, with quantum fluctuations seeding density perturbations. Upcoming observations are expected to decide between qualitatively different classes of inflationary dynamics. For example, the tensor to scalar ratio is closely related to the field range of the inflaton, and non-Gaussianity can distinguish between slow-roll versus more general single field inflation, and single-field versus multiple field inflation. The sensitivity of primordial inflation to Planck-suppressed operators also provides a small but nontrivial opportunity to connect cosmological observations with the structure of the UV completion of gravity (for which string theory provides a candidate in which several inflationary mechanisms and signatures have been developed.) Finally, exploration of potential alternatives to inflation continues.

At the same time, theorists are grappling with the challenge of formulating cosmology in a precise way, a task rendered nontrivial by the existence of horizons and singularities. Several concrete approaches to this problem have emerged in recent years, suggesting new questions and calculations.

This program will pursue all of the above directions, as well as any others that may emerge along the way.