Towards Precision-Controlled Partonic Structures from First Principles

Abstract

The internal structure of hadrons is governed by nonperturbative Quantum Chromodynamics (QCD). This dissertation presents first-principles calculations of partonic observables using lattice QCD and effective field theory, with controlled systematic uncertainties, advancing from collinear structure to transverse-momentum-dependent distributions (TMDs) that encode the three-dimensional partonic structure of hadrons. Within the large momentum effective theory (LaMET) framework, this work presents state-of-the-art calculations of pion distribution amplitudes and systematic studies of nucleon parton distributions, with control of renormalization, excited-state contamination, Fourier-transform systematics, and power corrections. A Coulomb-gauge formulation of quasi-distributions simplifies ultraviolet structure by avoiding Wilson-line related linear divergences, with Gribov-copy effects found to be negligible at current statistical precision. Building on these developments, this dissertation reports lattice determinations of nucleon TMD parton distributions, the Collins-Soper kernel, the intrinsic soft function, and pion TMD observables. These results provide nonperturbative inputs for global QCD analyses and the precision hadron-structure program, including the Electron-Ion Collider. In parallel, this work explores machine-learning acceleration of lattice gauge simulations through neural field transformations embedded in Hybrid Monte Carlo. In two-dimensional U(1) tests, the method reduces autocorrelation and improves performance toward finer lattice spacing, suggesting potential applications to more efficient lattice QCD simulations.