Probing the Nonperturbative Physics of QCD with Normalizing Flows and a moderate number of Pions

Abstract

Quantum Chromodynamics (QCD) is a cornerstone of the standard model of particle physics, and the best known theory of strong nuclear interactions. The only known systematically improvable ab-initio method for accessing the nonperturbative physics of QCD is Lattice QCD is, and this thesis presents two advances in our understanding QCD using lattice-based methods. The first is a calculation using many-pion systems to map out the entire zero temperature, nonzero isospin density region of the QCD phase diagram. The calculation uses novel methods for working with many-pion systems that enables working with thousands of pions, and furthermore provides rigorous constraints on the baryon-dense region of the QCD phase diagram. The second is an application of methods from machine learning (namely normalizing flows) in order to accelerate sampling. This approach has the promise of eliminating issues such as critical slowing down, as well as introducing novel tools and methods that enable methods of calculation that would be possible otherwise.