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(gπNN2). The same analysis reveals certain relationships between the two graphs. The two graphs are expressed as convolutions of the pion [gπ(y)] and the nucleon [gN(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 πNN vertex function and they turn out to have remarkably similar shapes. It is shown that this universality of gN(y) persists in a wide class of models. Such universal gN(y) peaks at y0=1-mπ/MN=0.85 and allows a simple parton model interpretation. Furthermore, the normalized smearing functions approximately satisfy the Berger-Coester-Wiringa-Thomas ansatz gπ(y)=gN(1-y) for two of the three models examined. Strong constraints on the nucleon off-shell dependence of the πNN vertex function [gπNN(pN2)] are obtained using the observed Gottfried sum rule violation as empirical input