Quantum Field Theory and Cosmology

University Of Florida, Gainesville FL

Investigators

Abstract

This award supports work at the interplay between quantum field theory and cosmology. A central prediction of quantum mechanics is that every degree of freedom has an irreducible minimum amount of motion. Under ordinary conditions quantum fluctuations emerge at random locations in space, persist for a brief time, and then disappear as new fluctuations emerge at other locations. However, a central prediction of cosmology is that the very early universe underwent a phase of accelerated expansion known as "primordial inflation". Quantum fluctuations of gravitational fields which emerge during primordial inflation persist indefinitely, and their strength builds up as new fluctuations emerge. These fluctuations change how particles propagate, how forces depend on space and time, and even how fast the universe expands. Although exact computations are not possible, the standard method of successive approximations shows that these effects grow with time, and with separation in the case of force laws, until they become so strong that standard computational techniques break down. Some researchers doubt the reality of this conclusion because gravitational fields can give different results in different coordinate systems, like the famous Schwarzschild singularity at the event horizon of a black hole, which is really an artifact of bad coordinates. Establishing that the effects of quantum fluctuations from inflation are real, and devising a procedure for extrapolating them to regimes in which they are strong, has the potential to revolutionize fundamental theory. In particular, this project will establish whether or not some of the outlandish parameters (e.g., less than 5% of the current energy density composed of normal matter) that seem to describe our current universe can be explained by quantum effects which became strong during the phase of primordial inflation. This project will also promote teaching, training and learning. Although the PI's current and past graduate students were selected for proven ability, it is worth noting that half of them are either female or Hispanic. During the course of this project the PI and his graduate students will collaborate with Professors Shun-Pei Miao (Taiwan), Tomislav Prokopec (Holland) and Nikolaos Tsamis (Greece) on (1) demonstrating that the effects of gravitational fluctuations are not coordinate artifacts; (2) developing a technique for extrapolating them to regimes where they become strong; (3) modeling these phenomena using low energy effective field theory in the sense of Donoghue; and (4) studying comparable effects from other fields. Although there will be some numerical work, most of the analysis will be analytic and will employ the Schwinger-Keldysh formalism, the renormalization group, Starobinsky's stochastic formalism and cosmological perturbation theory. Establishing that quantum gravitational fluctuations from primordial inflation induce measurable effects during the current epoch would revolutionize fundamental theory. Among other things, this has the potential to explain what caused primordial inflation, why the current universe is undergoing accelerated expansion and why Milgrom's MOdified Newtonian Dynamics (MOND) gives such an accurate description of galactic structure. 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.