Studies of the behavior of quantum chromodynamics (QCD) both on the lattice (DeTar) and in the infrared sector (Ball) form a major part of the efforts of the particle theory group. In lattice gauge calculations the quantum fields describing quarks and gluons are represented at discrete points in space and time. With such an approximation it becomes possible to carry out a numerical simulation of QCD and solve problems that have not yet yielded to a pencil-and-paper approach. By extrapolating the behavior of the system as the discrete lattice spacing is reduced (approximating continuous spacetime), it is possible to show that QCD indeed is capable of accounting for quark and gluon confinement. It is also possible to make predictions about the high-temperature behavior of quark-gluon plasmas. These simulations are carried out on the largest computers available in the United States.

Using an analogue to the low-energy behavior of bound heavy quark states, that of dual superconductors (in which it is the electric flux rather than the magnetic flux that is confined), effective interaction potentials for heavy quarks have been derived. With these potentials, QCD can be directly applied to the problem of the calculation of the heavy quark masses.

Recent investigations of the role of topology in field theory (Wu) have uncovered some important new phenomena that straddle the boundary between condensed matter physics and elementary particle physics: fractional statistics (systems that are neither bosonic or fermionic), the quantum Hall effect, Berry's phase (manifested by observable Aharanov-Bohm effects that arise purely from the geometric structure of certain Hamiltonians), Chern-Simons gauge theory and its relationship to string theory, and on the time variation of the gravitational constant that naturally arises in superstring theories. Topological aspects of physical phenomena and the geometric and algebraic structures of physical laws are among Wu's principal interests. The search for a deeper synthesis of the fundamental forces of nature may very well depend on such mathematical insights.