QCD Phenomenology and Light-Front

A natural calculus for describing the bound-state structure of relativistic compos-ite systems in quantum eld theory is the light-front Fock expansion which encodes the properties of a hadrons in terms of a set of frame-independent n−particle wave-functions. Light-front quantization in the doubly-transverse light-cone gauge has a number of remarkable advantages, including explicit unitarity, a physical Fock expan-sion, the absence of ghost degrees of freedom, and the decoupling properties needed to prove factorization theorems in high momentum transfer inclusive and exclusive reactions. A number of applications are discussed in these lectures, including semilep-tonic B decays, two-photon exclusive reactions, diractive dissociation into jets, and deeply virtual Compton scattering. The relation of the intrinsic sea to the light-front wavefunctions is discussed. Light-front quantization can also be used in the Hamil-tonian form to construct an event generator for high energy physics reactions at the amplitude level. The light-cone partition function, summed over exponentially-weighted light-cone energies, has simple boost properties which may be useful for studies in heavy ion collisions. I also review recent work which shows that the struc-ture functions measured in deep inelastic lepton scattering are aected by nal-state rescattering, thus modifying their connection to light-front probability distributions. In particular, the shadowing of nuclear structure functions is due to destructive in-terference eects from leading-twist diraction of the virtual photon, physics not included in the nuclear light-cone wavefunctions.