Speaker
Description
A fundamental question in hadron and nuclear physics is how the
mass scale for protons and other hadrons emerges from QCD, even in
the limit of zero quark mass. I will discuss a new approach to the
origin of the QCD mass scale and color confinement based on "lightfront
holography", a formalism which relates the bound-state
amplitudes in the fifth dimension of AdS space to the boost-invariant
light-front wavefunctions describing the structure of hadrons in
physical space-time. The result is a set of Poincarè-invariant boundstate
wave equations which incorporate quark confinement and
successfully predict many observed spectroscopic and dynamical features
of hadron physics, such as linear Regge trajectories with identical slope in
both the radial quantum number and the internal orbital angular
momentum. Generalizing this procedure using superconformal algebra
leads to a unified Regge spectroscopy of meson, baryon, and tetraquarks,
including remarkable supersymmetric relations between the masses of
mesons and baryons. The pion, although composite, is massless for zero
quark mass. One also can predict nonperturbative hadronic observables
such as structure functions, transverse momentum distributions, and the
distribution amplitudes defined from the hadronic light-front wavefunctions.
The analytic behavior of the QCD coupling controlling quark and gluon
interactions at large and small distances is also determined. The result is
an effective coupling defined at all momenta with a transition mass scale
which sets the interface between perturbative and nonperturbative hadron
dynamics. One also obtains a relation between the perturbative QCD
mass scale and hadron masses. I will also briefly discuss how conformal
constraints lead to the elimination of the renormalization scale ambiguity for
perturbative QCD calculations.
