This grant funds the research activities of Professor Sarah Shandera at The Pennsylvania State University.
By observing cosmological phenomena, physicists study the fundamental forces (including gravity) across many orders of magnitude in energy scale. In this way, and thanks to complementarity with terrestrial collider experiments, numerous successes in our understanding of the universe have been achieved. Unfortunately, the most puzzling cosmological phenomena are those that we cannot easily explore with colliders, including dark energy and the physics of the Big Bang era. The fundamental energy scales involved in those cases make laboratory tests impossible for the foreseeable future. As part of her research activities, Professor Shandera will develop a framework for robust inference of the underlying physical laws that correctly accounts for the types of uncertainty inherent in, but not unique to, cosmology. Together with her graduate students, she will study theories of the very early universe where unobservable physics may add uncertainty to the model. She will study both classical and quantum aspects of the problem. These studies will advance the national interest by contributing to our understanding and discovery of physical law at a fundamental level. Professor Shandera will involve her graduate students in communicating methods and results from the study of the universe to the public through workshops for middle- and high-school students and teachers.
More specifically, Professor Shandera will study systems in cosmology and particle physics where only a subset of stochastic or quantum-mechanical degrees of freedom are observationally accessible, and where that subsystem is coupled to unobserved modes. She will (1) explore how cosmic variance from coupling sub-Hubble modes to super-Hubble modes can affect inference about the inflationary era from upcoming observations of the polarization of the cosmic microwave background and large-scale structure surveys; (2) examine the quantum correlations in systems with long-short mode coupling and effective theories for short-wavelength modes with the long-wavelength modes traced out; and (3) use known issues and results from studies of multi-field inflation to explore effective theories for other quantum subsystems where the relevant unobserved modes need not be high-energy modes.