The gluon spin in the chiral bag model

We study the gluon polarization contribution at the quark model renormaliza tion scale to the proton spin, Gamma, in the chiral bag model. It is evalua ted by taking the expectation value of the forward matrix element of a loca l gluon operator in the axial gauge A(+) = 0. It is shown that the confinin g boundary condition for the color electric field plays an important role. When a solution satisfying the boundary condition for the color electric fi eld, which is not the conventionally used but which we favor, is used, the Gamma has a positive value for all bag radii and its magnitude is comparabl e to the quark spin polarization. This results in a significant reduction i n the relative fraction of the proton spin carried by the quark spin, which is consistent with the small flavor singlet axial current measured in the EMC experiments. (C) 2000 Published by Elsevier Science B.V.