Dynamic versus Static Hadronic Structure Functions

“Static” structure functions are the probabilistic distributions computed from the square of the light-front wavefunctions of the target hadron. In contrast, the “dynamic” structure functions measured in deep inelastic lepton-hadron scattering include the effects of rescattering associated with the Wilson line. Initial- and final-state rescattering, neglected in the parton model, can have a profound effect in QCD hard-scattering reactions, producing single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, the breakdown of the Lam-Tung relation in Drell-Yan reactions, nuclear shadowing, and non-universal nuclear antishadowing—novel leading-twist physics not incorporated in the light-front wavefunctions of the target computed in isolation. I also review how “direct” higher-twist processes – where a proton is produced in the hard subprocess itself – can explain the anomalous proton-to-pion ratio seen in high centrality heavy ion collisions.