Research Interests
Professor Stewart’s research interests involve theoretical nuclear and particle physics. In particular, he focuses upon the development and application of effective field theories to answer fundamental questions about interactions between elementary particles, including weak and electromagnetic interactions, and in particular strong interactions described by Quantum Chromodynamics (QCD).
The idea of an effective field theory is to determine the relevant degrees of freedom and symmetries of a system and combine this with a power counting expansion to derive an efficient and precise field theory framework for calculations.
Professor Stewart is a co-inventor of the Soft-Collinear Effective Theory (SCET), a field theory that separates short and long distance physics in processes involving energetic collisions of quarks, gluons, and other particles. This formalism makes it possible for a universal set of tools to handle a wide range of physics probed at proton and electron colliders, including jet physics, B meson physics, quarkonia production, and nuclear physics.
Professor Stewart has also contributed in the areas of Quasi-Distributions (for Lattice calculations of parton distribution functions), Heavy Quark Effective Theory (for b quark decays), Non-Relativistic QCD and QED (for heavy quark-antiquark systems and atomic systems like Hydrogen and positronium), and Nucleon Effective Theory (for two nucleon or deuteron systems interacting with low energy pions).
A major focus of Stewart’s current work is on theoretical ingredients needed to describe proton collisions at the Large Hadron Collider (LHC). Examples include his work on Higgs production and jet production.