Chiral quark model of nucleon spin-flavor structure with SU(3) and axial-U(1) breakings

The chiral quark model with a nonet of Goldstone bosons can yield an adequate description of the observed proton flavor and spin structure. In a previous publication we have compared the results of an SU(3) symmetric calculation with the phenomenological findings based on experimental measurements and SU(3) symmetry relations. In this paper we discuss their SU(3) and axial U(1) breaking corrections. Our result demonstrates the broad consistency of the chiral quark model with the experimental observations of the proton spin-flavor structure. With two parameters, we obtain a very satifactory fit to the $F/D$ ratios for the octet baryon masses and for their axial vector couplings, as well as the different quark flavor contributions to the proton spin. The result also can account for not only the light quark asymmetry $ū-\overline{d}$ but also the strange quark content $\overline{s}$ of the proton sea. SU(3) breaking is the key in reconciling the $\overline{s}$ value as measured in the neutrino charm production and that as deduced from the pion nucleon $\sigma$ term.