The spin of the proton in a hybrid chiral bag model

Abstract

We analyse the quark contributions to the proton spin in a hybrid chiral bag model which interpolates between the naive quark model and the Skyrme model. Care is taken to implement directly the anomalous axial U(1) symmetry. The total quark contribution to the proton spin varies rapidly with the bag radius R. If perturbative gluon corrections are neglected, recent EMC data on the quark spins constrain R to be less than 0.5 fm.