Physical effects of hadronic bremsstrahlung: Reactions at large and small momentum transfers

The synthesis of Regge behavior and other hadronic features with the parton model is discussed. Regge behavior of electromagnetic and weak amplitudes is shown to be a consequence of hadronic bremsstrahlung and the Regge behavior of hadronic amplitudes. A characterization of the hadronic wave function in terms of two components is emphasized. One component, which arises from the constituents of the hadronic bremsstrahlung, yields the wee-parton spectrum and Regge behavior and falls rapidly as any one constituent is constrained to take most of the momentum of the incident hadron. The second component, which is hadron irreducible, and most probably involves the minimum number of parton constituents, must have approximately power-law falloff in invariant variables. Only this second component contributes to large-angle exclusive scattering, the form factors at large $t$, and the scaling structure function for $x$ near 1. This component is responsible for the Drell-Yan-West relation and yields simple crossing to the annihilation channel at $x\sim 1$. Our approach and analysis clarify the nature of the impulse approximation in hadronic scattering. For example, the dramatic fixed-pole nature of the Compton amplitude at large $t$ is discussed and its importance is emphasized.