Quantum Field Theory and Cosmology

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Observational cosmology has provided the first-ever data on quantum gravity, and this is catalyzing the difficult passage of the subject from speculation to hard science. Conversely, quantum gravity has the potential to help resolve some of the great puzzles which confront cosmology, including: (a) What caused the initial spurt of expansion at the birth of the universe and how can it be tested? (b) Can modifications of Einstein's gravity theory dispense with the huge undetected and exotic contributions to the current energy density (95% of the total!) needed to account for galaxies, galaxy clusters and for the overall expansion of the universe? This project examines novel solutions to these questions. It will additionally promote teaching, training and learning. The PI's success in teaching has been recognized by awards at his own institution and by the American Physical Society. More than half the PI's current and past graduate students belong to under-represented groups, including two who are filling vital STEM educational positions within the United States. The PI has also been very active in outreach, with highly-cited review articles and numerous popular colloquia.The PI's group will continue their collaborations with Prof. Shun-Pei Miao (NCKU, Taiwan), Prof. Tomislav Prokopec (U. Utrecht, Netherlands) and Prof. Nikolaos Tsamis (U. Crete, Greece) to pursue analytical and numerical research in four areas: (1) Phenomenology of perturbations --- exploit the newly-derived functional dependence to reconstruct the geometry from data and to design new statistics which maximize non-Gaussianity from features in the power spectrum. (2) Quantum back-reaction on inflation --- extend the functional dependence to Standard Model fields to study how their couplings to the inflaton would modify inflation, and exploit recent progress in renormalizing nonlocal observables to study how inflationary gravitons modify inflation. (3) Nonlocal models of gravity --- study structure formation in the PI's nonlocal modified gravity model which dispenses with dark matter, and resolve a paradox in how the PI's nonlocal cosmology model contrives to describe structure formation better than general relativity. (4) Quantum loop effects --- exploit recent progress in removing the gauge dependence in calculations of how gravitons modify particle kinematics and long range forces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.