Dynamical Mechanisms for Supersymmetry Breaking
R. G. Leigh*
U.S. Department of Energy, DE-FG02-91ER40677

Supersymmetry is thought to be a desirable property of microscopic theories which subsume the Standard Model of particle physics. In order that it be consistent with present day experiments, supersymmetry must be a broken symmetry. Field theory models which dynamically break supersymmetry are being studied with the hope of understanding the mechanism more fully and applying it to realistic situations.

Elementary Particle Theory
A. X. El-Khadra,* R. G. Leigh,* S. S. Willenbrock,* M. Rozali, T. Stelzer, C. Bouchard, M. Gilson, V. Jejjala, A. Ostling, K. Paul, M. Smith, Z. Sullivan
U.S. Department of Energy, DE-FG02-91ER04677

The high-energy theory group has a wide variety of research interests. Topics include the top quark, electroweak symmetry breaking, quantum chromodynamics and lattice field theory, standard-model phenomenology, dynamical supersymmetry breaking, duality in supersymmetric field theory and string theory, M theory, and grand unification.

Lattice Field Theory
J. B. Kogut,* P. Vranas
National Science Foundation, PHY 96-05199

In the theory called quantum chromodynamics, observed particles such as the proton are composed of quarks, held together by forces transmitted by gluons, described by a nonabelian gauge field. To calculate one uses simulation techniques on a space-time lattice. New methods for dealing with fermions in lattice gauge theories have been developed by our group and are now being extensively exploited to study chiral symmetry restoration and quark deconfinement at finite temperatures and chemical potential and to study particle spectra. Quantum electrodynamics and fluctuating surfaces are also under investigation.

Nonperturbative Aspects of Supersymmetric Quantum Field Theories
R. G. Leigh*
University of Illinois

The study of supersymmetric field theories is of great interest, since it is possible to obtain exact nonperturbative information, which may be of use in understanding the strong coupling regime of realistic field theories. There is an important property, known as duality, which connects the physical observables of one field theory to another. The full consequences of duality in non-Abelian gauge theories is only now being worked out.

Standard Model Phenomenology with Lattice QCD
A. X. El-Khadra,* Z. Sroczynski
U.S. Department of Energy, DE-FG02-91ER40677; Alfred P. Sloan Foundation

Quantum chromodynamics (QCD), the theory of the strong interactions, is amenable to perturbative calculations only at high energies. A quantitative understanding of the low-energy behavior of QCD, like the interactions of quarks inside hadrons, requires nonperturbative methods. Lattice field theory offers a systematic approach to solving QCD nonperturbatively. The space-time continuum is replaced by a discrete lattice. Part of our research is concerned with improvements in the formulation of lattice QCD. Other projects deal with applications of lattice QCD to phenomenologically interesting processes that yield insight into the standard model of particle physics.

Strong and Electroweak Interactions
S. Willenbrock,* F. Maltoni, K. Paul, M. Niczyporuk
U.S. Department of Energy, DE-FG02-91ER40677 Task P

The top quark, discovered in 1995, is the most recently discovered fundamental particle of nature. It is much heavier than the other five known quarks and may therefore be exotic in some way. We perform theoretical calculations related to measurements, which will be made in the near future, to test the properties of the top quark. Hopefully these measurements will point the way to understanding nature at a deeper level. We are also studying the mechanism responsible for breaking the electroweak symmetry, which ultimately generates the masses of all elementary particles.

Studies in Quantum Field Theory
S.-J. Chang,* J. B. Kogut*
National Science Foundation, PHY 96-05199

Quantum field theory is the union of quantum mechanics and relativity theory. It provides a framework suitable for the study of the fundamental interactions of nature-the strong, the electromagnetic, and the weak interactions of the elementary particles. Research by the group includes (1) predictions of quantum chromodynamics, the natural generalization of electromagnetism for the structure of strongly interacting particles, (2) semiclassical approach, (3) physics at superhigh energies, and (4) other model field theories.

Superstring Theory
R. G. Leigh*
University of Illinois

Superstring theory is our only candidate for a consistent unification of quantum field theory and gravity. It provides a framework in which an understanding of the components of the standard model of particle physics may be sought. Research here includes studies of the nonperturbative aspects of string theory, including the special role played by D-branes, which are multidimensional solitonic states.