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Theoretical Particle Physics
^ 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 predictions of quantum chromodynamics, the natural generalization of electromagnetism for the structure of strongly interacting particles; semiclassical approach; physics at superhigh energies; and other model field theories.

^ Elementary Particle Theory
A. X. El-Khadra,* R. G. Leigh,* S. S. Willenbrock,* D. Berenstein, F. Maltoni, V. Jejjala, D. Menscher, M. Niczyporuk, K. Paul
U.S. Department of Energy, DEFG02-91ER04677

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.

^ Standard Model Phenomenology with Lattice QCD
A. X. El-Khadra,*
U.S. Department of Energy, DEFG02-91ER40677; 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 this 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.

^ 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 particle spectra chiral and to study symmetry restoration and quark deconfinement at finite temperatures and chemical potential. Quantum electrodynamics and fluctuating surfaces are also under investigation.

^ Dynamical Mechanisms for Supersymmetry Breaking
R. G. Leigh*
U.S. Department of Energy, DEFG02-91ER40677

Supersymmetry is thought to be a desirable property of microscopic theories that 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 that dynamically break supersymmetry are being studied with the hope of understanding the mechanism more fully and applying it to realistic situations.

^ 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.

^ Studies in Lattice Field Theory
J. Stack*
National Science Foundation, PHY99-00658

The primary purpose of this work is to gain a physical understanding of how quarks are confined inside nuclear particles or hadrons. Quantum chromodynamics is the theory describing quarks and their interactions, and the proposed work will involve supercomputer simulations of quantum chromodynamics. These simulations provide data unobtainable by other means, which can be used to provide a physical picture of the forces confining quarks. These forces underlie all the phenomena of nuclear physics and rank in importance with the more familiar forces of gravity and electromagnetism. The approach followed in this research is to look for what is called a topological explanation of confinement. This means that confinement is postulated to be due to a dense gas of topological objects. At present, attention is focused on either magnetic monopoles or center vortices as the relevant topological objects. The major challenge is to develop reliable methods for identifying these objects in the raw data of simulations and accurate methods of determining the confining forces from them.

^ Strong and Electroweak Interactions
S. Willenbrock,* F. Maltoni, K. Paul, M. Niczyporuk
U.S. Department of Energy, DEFG02-91ER40677 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. Researchers perform theoretical calculations related to measurements, which will be made in the near future, to test the properties of the top quark. The team is hopeful that these measurements will point the way to understanding nature at a deeper level. Researchers are also studying the mechanism responsible for breaking the electroweak symmetry, which ultimately generates the masses of all elementary particles.


Summary of Engineering Research