Study of Nucleon Spin Structure Functions based on an Effective Model of QCD

在手征夸克孤子模型的框架下，完成了未极化和纵向极化的twist-2部分子分布函数的理论计算。结果表明，除了Q^2演化的初始能量标度外，该模型不需要任何可调参数即可解释近期高能深非弹性散射观测的所有定性特征。它们包括F^p_2(X)-F^n_2(X)、F^n_2(X)/F^p_2(X)的NMC数据，d^^-(X)-u^-(X)数据的Hermes和E866数据，以及g^p_1(X)、g^n_1(X)和g^d_1(X)的EMC和SMC数据。通过将模型推广到SU(3)，给出了包括奇异夸克在内的核子中轻味海夸克分布的理论预测。重点研究了轻味海夸克的非对称性，如d^^-(X)-u^-(X)，d^-(X)/u^-(X)，Δu^-(X)-Δd^^-(X)以及粒子-反粒子…研究了S(X)-S^-(X)，S(X)/S^-(X)，ΔS(X)-ΔS^-(X)等人所代表的奇异夸克分布的更多对称性，并研究了与自旋有关的结构函数g_2(x，q^2)。结果表明，g_2(x，q^2)的扭度-3部分在q^2-5GeV^2能级范围内对总分布有不可忽略的贡献，但主要集中在较小的x区，因此质子和中子的三阶矩∫^1_0 x^2 g^-2(x，q^2)dx很小，与最近的E155数据一致。还给出了核子的扭转-2和扭转-3的手征奇数分布函数的预言。证明了在手征夸克孤子模型框架内适当考虑真空极化效应的重要性，证明了所谓的Soffe不等式不仅对夸克分布成立，而且对反夸克分布也成立。我们还成功地证明了非零夸克凝聚作为QCD真空手征对称性自发破缺的信号，在核子的手征奇扭度-3分布函数e(X)中，在x=0处产生了一个Delta函数奇点。E(X)中的这一奇点将被观察到是对一阶矩和规则的相当大的违反，然后被解释为给出了一种非常罕见的情况，即QCD的非平凡真空结构体现在局域QCD激发的可视区域，即核子中。较少

We have completed the theoretical calculation of the unpolarized and longitudinally polarized twist-2 parton distribution functions within the framework of the chiral quark soliton model. It was shown, that, without any adjustable parameter except for the initial-energy scale of the Q^2-evolution, the model can explain all the qualitatively noticeable features of the recent high-energy deep-inelastic Scattering observables. They include the NMC data for F^p_2(x) - F^n_2 (x), F^n_2(x)/F^p_2(x), the HERMES and E866 data for d^^-(x) - u^^-(x) data, and the EMC and SMC data for g^p_1(x), g^n_1(x) and g^d_1(x). We have also given theoretical predictions for the light-flavor sea-quark distributions in the nucleon including the strange quark one by extending the model to flavor SU(3). A particular emphasis of study is put on the light-flavor sea-quark asymmetry as exemplified by the observables d^^-(x) - u^^-(x), d^^-(x)/u^^-(x), Δu^^-(x) - Δd^^-(x) as well as on the particle-antiparticle asy … More mmetry of the strange quark distributions represented by s(x) - s^^-(x), s(x)/s^^-(x), Δs(x) - Δs^^-(x) etc. We also investigated the spin-dependent structure function g_2(x, Q^2). It turns out that the twist-3 part of g_2(x, Q^2) gives nonnegligible contributions to the total distributions at the energy scale of Q^2 - 5 GeV^2 but mainly in the small x region only, so that the corresponding third moment ∫^1_0 x^2 g^^-_2(x, Q^2) dx are pretty small for botb of the proton and neutron in conformity with the recent E155 data. Also given are the predictions for the twist-2 and twist-3 chirally-odd distribution functions of the nucleon. The importance of the vacuum polarization effects, which are properly taken into account within the framework of the chiral quark soliton model, is demonstrated by showing that the so-called Soffer inequality holds not only for the quark distributions but also for the antiquark ones. We have also succeeded in proving that the nonvanishing quark condensate as a signal of the spontaneous chiral symmetry breaking of the QCD vacuum brings about a delta-function singularity at x = 0 in the chirally-odd twist-3 distribution functions e (x) of the nucleon. This singularity in e (x), which would be observed as a sizable violation of the 1st moment sum rule, is then be interpreted as giving a very rare case that the nontrivial vacuum structure of QCD manifests in an obsrvable of a localized QCD excitation, i.e. the nucleon. Less