Cloudy bag model of the nucleon

A previously derived model in which a baryon is treated as a three-quark bag that is surrounded by a cloud of pions is used to compute the static properties of the nucleon. The only free parameter of the model is the bag radius which is fixed by a fit to pion-nucleon scattering in the (3,3)-resonance region to be about 0.8 fm. With the model so determined the computed values of the root-mean-square radii and magnetic moments of the neutron and proton, and $g_A$, are all in very good agreement with the experimental values. In addition, about one-third of the $\Delta$-nucleon mass splitting is found to come from pionic effects, so that our extracted value of ${\alpha }_s$ is smaller than that of the MIT bag model.