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

TL;DR

This paper models the electroweak structure of nucleons using a meson-cloud approach with light-cone wavefunctions, successfully describing form factors and internal charge distributions, highlighting the meson cloud's role at low momentum transfer.

Contribution

It introduces a detailed meson-cloud model with light-cone wavefunctions for nucleons, providing improved descriptions of electroweak form factors and internal quark distributions.

Findings

Good agreement with experimental form factors

Meson cloud effects are significant only at low Q^2

Neutron charge density shows a central negative charge

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 wavefunctions 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^2. Mixed-symmetry S'-wave components in the wavefunction 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, with 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.