Neutron Charge Density from Simple Pion Cloud Models

TL;DR

This paper models the neutron as a bare nucleon with a pion cloud to analyze its form factor and charge density, showing that a finite nucleon size is necessary for negative charge density at the center.

Contribution

It introduces simple pion cloud models with different form factors to explain neutron charge distribution, aligning qualitative results with experimental data.

Findings

Neutron form factor is negative definite for all Q^2.

Finite nucleon size is essential for negative central charge density.

Models achieve qualitative agreement with experimental measurements.

Abstract

The physical nucleon is modeled as a bare nucleon surrounded by a pion cloud using a psuedoscalar pion-nucleon coupling to examine its implications for the neutron form factor, F_1, and the corresponding transverse charge density in the infinite momentum frame. Two versions, one with a tunable Pauli-Villars parameter, and one with light-front cloudy-bag pion-nucleon form factors, are examined. A qualitative agreement with the experimental form factor (negative definite for all Q^2) and transverse charge density are achieved when the nucleon is treated as having a finite extent. The bare nucleon must have a finite extent if this model is to account for a negative definite F_1, and consequently a negative transverse charge density of the neutron at its center.