Axial exchange currents and the spin content of the nucleon in a nonrelativistic chiral quark model

Within the context of a nonrelativistics chiral quark model (XQM) where chiral symmetry is introduced via a non-linear sigma model, we evaluate the axial form factors gA3, gA8(0) and gA0(0) related to the quark spin content of the nucleon. Our calculation includes one-body (impulse approximation) and two-body (exchange currents) axial operators whose contributions satisfy Partial Conservation of Axial Current (PCAC) exactly. While gA3(0) is dominated by the impulse contribution we find significant corrections due to exchange currents effects in the evaluation of the other two quantities, gA8(0) and gA0(0). The results are in good agreement with experiments. In addition, the use of PCAC allows us to obtain couplings constants of the η and η' mesons to nucleons that are in good agreement with other determinations