Non-perturbative structure of the polarized nucleon sea

We investigate the flavour and quark-antiquark structure of the polarized nucleon by calculating the parton distribution functions of the nucleon sea using the meson cloud model. We find that the SU(2) flavor symmetry in the light antiquark sea and quark-antiquark symmetry in the strange quark sea are broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar. The polarization of the strange sea is found to be positive, which is in contradiction to previous analyses. We predict a much larger quark-antiquark asymmetry in the polarized strange quark sea than that in the unpolarized strange quark sea. Our results for both polarized light quark sea and polarized strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure

On the phenomenological analyses of ss-sˉ{\bar s} asymmetry in the nucleon sea

Two phenomenological models which give opposite predictions for the $s$-${\bar s}$ asymmetry in the nucleon sea are re-analyzed carefully. It is pointed out that although the quantitative results in both models depend dramatically on the parameters, the predictions for the shape of $s(x)-{\bar s}(x)$ in the two models are parameter independent and opposite. Thereby the coming experiments are likely to be able to distinguish the two models. We find that the reason for the two models giving opposite predictions is that the fluctuation functions and parametrizations for the strange (anti-strange) quark distribution in the baryon (meson) in the two models are quite different. To further investigate these models, we use the same parametrizations for the strange (anti-strange) distributions of the baryon (meson) in the two models. We find that one of the models depends strongly on the parameter which controls the behavior of the meson-baryon fluctuation function. Also the two models agree on the shape and size of $s$-${\bar s}$ for some values of the model parameters, but can disagree strongly for others.Comment: RevTex, 11 pages, 7 Postscript figure

Moments of isovector quark distributions from lattice QCD

We present a complete analysis of the chiral extrapolation of lattice moments of all twist-2 isovector quark distributions, including corrections from Nπ and Δπ loops. Even though the Δ resonance formally gives rise to higher order non-analytic structure, the coefficients of the higher order terms for the helicity and transversity moments are large and cancel much of the curvature generated by the wave function renormalization. The net effect is that, whereas the unpolarized moments exhibit considerable curvature, the polarized moments show little deviation from linearity as the chiral limit is approached