
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 (quarkantiquark bound states) containing a
heavy quark (charm or bottom) are studied by Professor ElKhadra. 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 CabibboKobayashiMaskawa
matrix element) from data, one must provide an accurate calculation of the
meson decay. Professor ElKhadra 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 (quarkantiquark bound states) is studied by
Professor ElKhadra. Accurate calculations of meson masses provide information
about quark masses and the strength of the strong interaction that binds the
quark and antiquark. Professor ElKhadra 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.
