From Hadronization to Strong CP: A Charcuterie Platter of QCD Matter

Two fundamental questions in theoretical physics are: How does the proton form? and What is dark matter?  In this talk, I will present my research, which uses effective field theory (EFT) methods to address both of these critical issues starting from the fundamental theory of the strong interactions, Quantum Chromodynamics (QCD). I will first discuss my work on heavy quark fragmentation as a tool for understanding hadronization — the process by which hadrons, such as protons, emerge from quarks and gluons. Using the fact that the heavy quark mass is much larger than the typical QCD interaction energy, I propose new sum rules based on heavy quark spin symmetry that can be tested at existing particle colliders. I will then turn to the strong CP (Charge-Parity) problem and the QCD axion solution, which introduces a hypothetical particle that could constitute dark matter. My work uncovers new tensions between the strong CP problem and the axion domain wall problem in cosmology, which place significant constraints on various QCD axion models. Finally, I will provide an overview of my other contributions to open challenges in QCD and outline my future research directions.