EXACT SYMMETRIES AND THE ROLE OF THE PION CLOUD IN DEEP-INELASTIC ELECTRON-NUCLEON SCATTERING

A careful analysis of exact symmetries, such as the charge conjugation symmetry and the electromagnetic and baryon current conservation, shows that exactly two nontrivial Feynman diagrams contribute to deep-inelastic inclusive pion electroproduction from the nucleon to O(g(pi-NN)2). The same analysis reveals certain relationships between the two graphs. The two graphs are expressed as convolutions of the pion [g(pi)(y)] and the nucleon [g(N)(y)] smearing functions and their respective deep-inelastic structure functions. The nucleon smearing functions are evaluated in three models of the nucleon off-shell dependence of the pi-NN vertex function and they turn out to have remarkably similar shapes. It is shown that this universality of g(N)(y) persists in a wide class of models. Such universal g(N)(y) peaks at y0 = 1 - m(pi)/M(N) = 0. 85 and allows a simple parton model interpretation. Furthermore, the normalized smearing functions approximately satisfy the Berger-Coester-Wiringa-Thomas ansatz g(pi)(y) = g(N)(1 - y) for two of the three models examined. Strong constraints on the nucleon off-shell dependence of the pi-NN vertex function [g(pi-NN)(p(N)2)] are obtainded using the observed Gottfried sum rule violation as empirical input.