The 2004 Nobel Prize in Physics again highlighted QCD, the fundamental theory of the strong interactions which underlies all the phenomena of nuclear physics, by recognizing the discovery of asymptotic freedom. The fact that the QCD coupling becomes weak at
short distance, and thus amenable to perturbation theory, has enabled confirmation of QCD with great precision in a variety of high energy phenomena. The complementary property of infrared confinement, whereby the coupling becomes strong at large distances, binds the quarks and gluons into the observed hadrons. However, this results in QCD becoming analytically intractable at low energy. Hence, even though we know that the properties of nucleons, nuclear forces and ultimately atomic nuclei are governed by QCD, there is no known analytical technique for calculating them. Lattice gauge theory provides the only rigorous approach to solving QCD in this low-energy regime. In particular, lattice QCD has reached a level of maturity in which we will be able to calculate physical observables with an accuracy that will allow unambiguous confrontation with hadronic data.
Among the key questions that lattice QCD, in concert with the experimental program, will address are:
What is the three-dimensional distribution of charge, current and spin within the nucleon?
What is the spectrum of excited mesons and baryons, and in particular those mesons containing explicit glue including glueballs and exotic mesons?
How does confinement work? What are the roles of monopoles, instantons and other classical QCD degrees of freedom?
To what extend can hadron-hadron interactions be understood directly from QCD?
These questions go to the heart of our understanding of the strong force, and all of them can be addressed withing the framework of
lattice QCD, either now or in the near future.
