“Electromagnetic” contribution to the nucleon spin

A possible resolution to the question of where the nucleon gets some portion of its internal angular momentum, not carried by the valence quarks, is given in terms of the electromagnetic field angular momentum of the nucleon. This field angular momentum is similar in origin to that of the Thomson dipole (an electric charge and a magnetic monopole), but arises from the interaction of the quark electric charges and magnetic dipoles. Rough, order of magnitude calculations show that such a field angular momentum could provide some of the nucleonʹs spin. Under assumptions similar to those used to calculate hadron mass splittings, QCD should also exhibit a similar field angular momentum coming from the interaction of color charges with color magnetic dipoles.