Theoretical Particle Physics

Part of Particle Physics

Anthony Duncan
Duncan’s research has focused primarily on nonperturbative aspects of quantum field theory, especially lattice field theory and more specifically lattice quantum chromodynamics (LQCD). LQCD is the only model-independent technique currently available for reliably computing nonperturbative features of the strong interactions. Duncan’s work in this area has focused on the physics of heavy-quark (B meson) systems, on the first determination of light quark masses fully including electromagnetic isospin effects in LQCD, and on detailed studies of the artifacts induced by the quenched approximation (in which virtual quark effects in QCD are neglected). Duncan has also studied a variety of analytic nonperturbative approaches, including resummation techniques such as the delta expansion, and applications of large N methods to a variety of models (most recently, noncompact sigma models).

More recently, Duncan’s research has broadened to include the application of field theory methods to the generalized Coulomb gas, a basic problem in modern biophysics, in which mobile charged entities move in a dynamical dielectric background. Methods originally developed for use in unquenched (full) QCD turn out remarkably to be of great utility in developing computationally efficient approaches to this problem. For more information, see the plenary talk delivered by Duncan at Lattice 2006, which can be found at http://www.physics.arizona.edu/lattice06.

Ayres Freitas

Freitas' research mostly deals with the phenomenology of new particles and interactions at colliders. One of the biggest questions in particle physics for several decades, the breaking of the electroweak symmetry and the stabilization of the electroweak scale, has inspired many new ideas like the Higgs mechanism, supersymmetry, extra dimensions, technicolor and little Higgs models. These models can be constrained by existing precision data and possibly could be discovered at future experiments, most notably at the Large Hadron Collider (LHC). Of special interest are precision analyses that would allow to reconstruct the underlying framework of a model from experimental data. Freitas has worked on methods to determine the spin and couplings of newly discovered particles, as well as ideas to detect particles that would be particularly elusive. One main focus has been on supersymmetric models, but also on models with extra dimensions, extended gauge groups and little Higgs models.

Some of the new physics models quite naturally could explain the origin of ordinary matter and/or dark matter in the universe. This opens up striking connections between collider physics and astrophysics and cosmology.

On the technical side, development of loop calculation techniques and Monte-Carlo tools are very important for the interpretation of the flood of new data expected from the LHC. Recently there has been much progress in both areas, leading to automated computer programs. Freitas has been working on methods for electroweak one- and two-loop calculations, as well as implementation of new models in Monte-Carlo generators.


Adam Leibovich
Leibovich’s research has mostly focused on applications of effective field theory techniques to phenomenological issues of relevance to current and future experiments. The main effective field theory used in this research has been the soft-collinear effective theory (SCET).

SCET has proven to be a remarkably effective theoretical tool for calculations of strongly interacting particles involving highly energetic particles. Kinematic situations precisely described by SCET occur at both current and future experiments, so the effective field theory can be used for the accurate calculations needed to compare theory to experiment. By using SCET, it has been possible to prove factorization theorems, sum large corrections which would otherwise render the theoretical prediction useless, and give new insight into older calculations, while at the same time allowing an estimate of the theoretical errors. Theoretical predictions based on model independent calculations together with the ability to make estimates of theoretical errors are necessary to interpret current and upcoming data from particle experiments.

The theoretical issues investigated range from heavy quark physics (under active investigation by the current so-called B factories) to LHC physics, which makes a connection to the activities of the experimental group. In particular, projects that Leibovich has already investigated include: B meson and Lb baryon decays, quarkonium (the bound state of a heavy quark–antiquark pair) production and decay, and effects of light quark masses in SCET. Recent talks on this research were given by C. Kim, a postdoc at the University of Pittsburgh, at the 2006 SCET Workshop (http://www.physics.arizona.edu/lattice06/) and by Leibovich at the ETC workshop on Heavy Quarkonium and Related Heavy Quark States (http://www.ect.it/).

Eric Swanson
Swanson’s research seeks to develop methods and phenomenology relevant to nonperturbative QCD. His research program has a number of related projects: Heavy Quark Phenomenology, Coulomb Gauge QCD, and Lattice Study of QCD Vacuum Structure.

The heavy quark phenomenology program includes studies of charmonium spectroscopy, molecules such as the X(3872), charmonium electromagnetic form factors and decay constants, electroweak transition form factors, and strong interaction effects in exclusive B decays. The chief effort is devoted to developing relativistic bound state models which are consistent with Ward-Takahashi identities and low energy theorems.

Coulomb gauge QCD, a many-body formalism that is capable of describing strongly interacting QCD, is under development. The formalism is based on the QCD Hamiltonian in Coulomb gauge and is designed to provide an efficient starting point for the bound state problem by summing leading infrared divergent diagrams and constructing efficient Fock space bases. The success of applications to glueball and meson spectra, ghost and gluon propagators, and the Wilson loop potential all point to the promise of the method. Current work is focused on refining the description of heavy quarkonia and on developing the finite temperature formalism.

The structure of the QCD vacuum underpins the crucial properties of confinement and chiral symmetry breaking. Lattice gauge theory is ideal for studying the QCD vacuum. Current efforts focus on an examination of the impact of vortex gauge configurations on the Wilson loop confinement potential, the topological susceptibility, adiabatic hybrid potentials, and the glueball spectrum.

Frank Tabakin
Frank Tabakin, professor emeritus, continues his research in the areas of electromagnetic production; hadron spectroscopy; and quantum information/computing.