String Theory

Research in string theory at Illinois is lead by Professors Katz and Leigh. We have an active group of postdocs and students, both graduate and undergraduate, with weekly meetings and seminars. More information on our activities can be found at the String Theory Group website. In particular, see our BCDE Seminar web page.

Weak interaction

The weak interaction of mesons (quark-antiquark bound states) containing a heavy quark (charm or bottom) are studied by Professor El-Khadra. These mesons decay via the weak interaction, which changes one type of quark into another. This transition involves a mixing parameter which must be measured experimentally. To extract this parameter (called a Cabibbo-Kobayashi-Maskawa matrix element) from data, one must provide an accurate calculation of the meson decay. Professor El-Khadra uses nonperturbative methods (lattice gauge theory) to perform such calculations.
The weak interaction of the top quark and the hypothetical Higgs boson are studied by Professor Willenbrock. The top quark is the heaviest known particle, and its weak interaction will be studied at the Fermilab Tevatron via processes that Professor Willenbrock has calculated. The Higgs boson, which is believed to be responsible for the spontaneous symmetry breaking of the weak interaction, will also be sought at the Tevatron via processes that Professor Willenbrock has calculated. Similar calculations have been performed for the CERN Large Hadron Collider, the heir to the Tevatron.

Strong interaction

The strong interaction of mesons (quark-antiquark bound states) is studied by Professor El-Khadra. Accurate calculations of meson masses provide information about quark masses and the strength of the strong interaction that binds the quark and antiquark. Professor El-Khadra uses lattice gauge theory to perform accurate nonperturbative calculations of meson masses.
Quarks are permanently confined within mesons (as well as baryons, which consist of three quarks). It is widely believed that the mechanism for this confinement is analogous to superconductivity. In the same way that a superconductor expels magnetic fields, the vacuum expels the field lines of the strong interaction. This confines these field lines to the interior of mesons and baryons. Professor Stack performs nonperturbative calculations, using lattice gauge theory, to support this model of confinement.
Quarks are subjected to high pressure and temperature in the interior of neutron stars, as well as at the Brookhaven Relativistic Heavy Ion Collider. Professor Kogut uses lattice field theory to perform nonperturbative calculations of quarks under such extreme conditions.
At high energies, the strong interaction is sufficiently weak that perturbation theory is valid. Professor Willenbrock performs perturbative calculations in the strong interaction to yield precise predictions for processes that will be measured at the Fermilab Tevatron and the CERN Large Hadron Collider.