Color Confinement, Hadron Dynamics, and Hadron Spectroscopy from Light-Front Holography and Superconformal Algebra

摘要

The QCD light-front Hamiltonian equation H-LF vertical bar Psi > = M-2 vertical bar Psi=Psi > derived from quantization at fixed LF time tau = t + z/c provides a causal, frame-independent method for computing hadron spectroscopy as well as dynamical observables such as structure functions, transverse momentum distributions, and distribution amplitudes. The QCD Lagrangian with zero quark mass has no explicit mass scale. de Alfaro, Fubini, and Furlan (dAFF) have made an important observation that a mass scale can appear in the equations of motion without affecting the conformal invariance of the action if one adds a term to the Hamiltonian proportional to the dilatation operator or the special conformal operator. If one applies the dAFF procedure to the QCD light-front Hamiltonian, it leads to a color-confining potential kappa(4)zeta(2) for mesons, where zeta(2) is the LF radial variable conjugate to the q (q) over bar invariant mass squared. The same result, including spin terms, is obtained using light-front holography, the duality between light-front dynamics and AdS(5), if one modifies the AdS(5) action by the dilaton e(kappa 2z2) in the fifth dimension . When one generalizes this procedure using superconformal algebra, the resulting light-front eigensolutions provide a unified Regge spectroscopy of meson, baryon, and tetraquarks, including remarkable supersymmetric relations between the masses of mesons and baryons and a universal Regge slope. The pion q (q) over bar eigenstate has zero mass at m(q) = 0. The superconformal relations also can be extended to heavy-light quark mesons and baryons. This approach also leads to insights into the physics underlying hadronization at the amplitude level. I will also discuss the remarkable features of the Poincare invariant, causal vacuum defined by light-front quantization and its impact on the interpretation of the cosmological constant. AdS/QCD also predicts the analytic form of the nonperturbative running coupling alpha(s)(Q(2)) mu e(-Q2/4 kappa 2). The mass scale kappa underlying hadron masses can be connected to the parameter Lambda((MS) over bar) in the QCD running coupling alpha(s)(Q(2)) by matching the nonperturbative dynamics to the perturbative QCD regime. The result is an effective coupling defined at all momenta. One obtains empirically viable predictions for spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions. Finally, I address the interesting question of whether the momentum sum rule is valid for nuclear structure functions.