Electroweak structure of the nucleon, meson cloud, and light-cone wave functions

Abstract

The meson-cloud model of the nucleon consisting of a system of three valence quarks surrounded by a meson cloud is applied to study the electroweak structure of the proton and neutron. Light-cone wave functions are derived for the dressed nucleon as pictured to be part of the time a bare nucleon and part of the time a baryon-meson system. Configurations are considered where the baryon can be a nucleon or a {delta} and the meson can be a pion as well as a vector meson such as the {rho} or the {omega}. An overall good description of the electroweak form factors is obtained. The contribution of the meson cloud is small and only significant at low Q{sup 2}. Mixed-symmetry S{sup '}-wave components in the wave function are most important to reproduce the neutron electric form factor. Charge and magnetization densities are deduced as a function of both the radial distance from the nucleon center and the transverse distance with respect to the direction of the three-momentum transfer. In the latter case, a central negative charge is found for the neutron. The up and down quark distributions associated with the Fourier transform of the axial form factor have opposite sign, withmore » the consequence that the probability to find an up (down) quark with positive helicity is maximal when it is (anti)aligned with the proton helicity.« less