Prof.
Stanley J. Brodsky
(SLAC National Accelerator Laboratory, Stanford University)

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 bound-state
wave equations which incorporate quark confinement and
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 bound-state, 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.

### Summary

I will discuss a new approach to the

origin of the QCD mass scale and color confinement based on "light-front

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 bound-state

wave equations which incorporate quark confinement and

predict many observed spectroscopic and dynamical features

of hadron physics.

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.

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.