UNC-CH Physics and Astronomy Thesis Proposal Presentation

Nolan Miller

“Ab initio calculations of hadronic quantities using lattice quantum chromodynamics”

Quantum chromodynamics (QCD) is the quantum field theory describing hadronic matter, which comprises the majority of the non-dark energy-density of our universe. But unlike quantum field theories such as quantum electrodynamics, the coupling constant of QCD increases at low temperatures, making perturbative calculations using Feynman diagrams impossible. Instead we must resort to lattice QCD, in which the infinite dimensional path integral over all of spacetime becomes a high dimensional integral restricted to a discretized, periodic box.

In my talk, I will summarize the properties of the lattice action used by my collaboration and present preliminary results obtained from using it. First I will present my results on scale setting, which describes how we can convert a dimensionless (lattice) value into something dimensionful (physical). Next I will explain my calculation of the ratio of the kaon and pion pseudoscalar decay constants, from which we can glean insight into the V_us matrix element of the CKM matrix. Then I will describe my fits of the hyperon mass spectrum, and in the process, I will explain how to determine various low energy constants of the hyperon effective field theories from which the hyperon mass formulae were derived. In principle, such effective field theories could be used to make predictions about physical processes (eg, hypeon-nucleon interactions in neutron stars) that are difficult or impossible to observe experimentally. Finally I will present some work on fitting the nucleon axial charge, a fundamental property of nucleons which determines their rate of beta decay, and show how I intend expand on this work to calculate the hyperon axial charges.