Three-Quark Currents and Baryon Spin

We show that three-quark axial currents as required by broken SU(6) spin-flavor symmetry reduce the quark spin contribution to proton spin from Σp=1 (one-quark axial current value) to Σp=0.41(12) consistent with the empirical value Σp,exp=0.33(08). In the case of the Δ+(1232) baryon, we find that three-quark axial currents increase the one-quark axial current value ΣΔ+=3 to ΣΔ+=3.87(22). We also calculate the quark orbital angular momenta Lu and Ld in the proton and Δ+ and interpret our results in terms of the prolate and oblate geometric shapes of these baryons consistent with their intrinsic quadrupole moments. (author)