Organizers:
Dam T. Son
son@phys.washington.edu
Misha Stephanov
misha@uic.edu
Matthew Strassler
strassler@physics.rutgers.edu
Derek Teaney
derek.teaney@stonybrook.edu
Program Coordinator:
Laura Lee
lee@phys.washington.edu
(206) 685-3509
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Workshop: String Methods
for the Real World
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From Strings to Things: String Theory Methods in QCD and Hadron Physics
March 24 - June 6, 2008
Inca Quipu, Larco Museum
The interest in the applications of AdS/CFT techniques to QCD has
exploded recently. One of the goals of this program is to bring
coherence into this rapidly developing new field by comparing
different approaches and ideas while grounding them firmly into the
fundamental formalism.
A wide range of topics are currently under development, and
several more seem likely to come within reach. We briefly
mention a few of these topics below.
Hadron Physics Modeling and AdS/QCD
An important development in the AdS/CFT correspondence is the
introduction of a simple method for adding quarks
in fundamental representation to the original AdS/CFT setting. This
technical advance has made it possible to construct analytically
tractable models whose hadrons are very similar to that of QCD. A
complementary approach has also emerged, which attempts to construct
phenomenologically viable five-dimensional models of hadrons in QCD in
a "bottom-up" fashion. During the program we plan to discuss these
approaches.
Finite Temperature and Finite Density
Thermodynamic and kinetic observables of strongly coupled gauge
plasmas which have gravity duals can be computed using the AdS/CFT
correspondence. In these theories the viscosity to entropy ratio is
universal and small. The value of this ratio has attracted
considerable attention since the collective flow observed at RHIC
implies a similarly small transport time scale in thermal
QCD. Further, the AdS/CFT correspondence has been used to compute the
energy loss of a heavy quark moving in a hot gauge plasma and the
"jet-quenching parameter." In addition, many questions remain. For
example, can gravity duals describe the dynamics of this
thermalization? Should one expect AdS/CFT techniques to be less
relevant or more relevant at LHC energies?
High Energy Scattering
One of the historical connections between string theory and QCD is in the
large s, fixed t regime of high-energy scatterings, where
data can be fit with a soft Pomeron Regge trajectory. Recently there has
been a lot of interest in high-energy scattering, black holes as
fireballs, and the eikonal approximation.
Within the context of single Pomeron exchange, deeper formal
connections between the strong-coupling results of string theory and
the work of experts on the perturbative hard Pomeron are still being
uncovered. Beyond this, there are nonlinear effects involving
multi-Pomeron exchange which remain to be understood.
The work on Pomerons is relevant for various issues in heavy ion physics.
Overcoming the Limitations of Gauge/Gravity Duality
The original example of gauge/gravity duality N=4
super-Yang-Mills theory, which is a conformal, and not confining,
field theory. Several years ago it was shown how to
deform this theory to make it more similar to QCD; theories with
confinement,
chiral symmetry breaking, and other key features of QCD have
been found that have string theoretic dual descriptions. However, in
order for the dual description to be tractable, the 't Hooft coupling
of the gauge theory has to be large all the way to the
ultraviolet, in contrast with the asymptotic freedom of QCD.
To make closer contact with QCD, more details of string theory on
highly curved spaces must be understood. This is a very difficult
string theory problem, but slow progress is currently being made in
a number of contexts.
General AdS/CFT Formalism Questions
There have been many discoveries in the formal aspects of
gauge/gravity and gauge/string duality that could be of potential use
for QCD, and many theoretical developments await active study.
Interesting topics would include the role of approximate conformal
invariance, the appearance of hidden integrability (perhaps in new as
well as known contexts), and special features of the large-Nc and
large 't Hooft coupling expansions. Other questions of great
importance involve the universality, or lack theorof, of results
obtained in the AdS/CFT correspondence. The gauge/string
correspondence can help us clarify which aspects of QCD are unique to
QCD, and which ones are true of larger classes of theories. It
therefore has the potential to greatly improve out conceptual
understanding of QCD.
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