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

在手性夸克孤子模型框架下，完成了非极化和纵向极化扭转-2部分子分布函数的理论计算。结果表明，除了Q^2演化的初始能量尺度外，该模型不需要任何可调参数，可以解释最近高能深非弹性散射观测的所有定性显著特征。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)的HERMES和E866数据，g^p_1(x)、g^n_1(x)和g^d_1(x)的EMC和SMC数据。我们还通过将模型扩展到味SU(3)，给出了核子中包括奇异夸克在内的轻味海夸克分布的理论预测。重点研究了轻味海夸克不对称性，如观测值d^^-(x) - u^^-(x)、d^^-(x)/u^^-(x)、Δu^^-(x) - Δd^^-(x)以及粒子-反粒子easy . s(x) - s^^-(x)、s(x)/s^^-(x)、Δs(x) - Δs^^-(x)等奇异夸克分布的更多对称性。我们还研究了自旋相关的结构函数g_2（x, Q^2）。结果表明，g_2（x, Q^2）的扭转-3部分在Q^2 - 5gev ^2的能量尺度上对总分布有不可忽略的贡献，但主要是在小的x区域，因此对应的第三矩∫^1_0 x^2 g^ -_2(x, Q^2) dx对于质子和中子都是相当小的，与最近的E155数据一致。同时给出了对核子的扭-2和扭-3手性奇分布函数的预测。真空极化效应的重要性在手性夸克孤子模型的框架内得到了适当的考虑，通过证明所谓的Soffer不等式不仅适用于夸克分布，也适用于反夸克分布来证明。我们还成功地证明了作为QCD真空自发手性对称性破缺的一个信号的非消失夸克凝聚在核子的手性奇捻-3分布函数e (x)中在x = 0处产生一个δ函数奇点。e (x)中的这个奇点，将被视为对第一矩和规则的相当大的违反，然后被解释为给出一个非常罕见的情况，即QCD的非平凡真空结构在可观测的局域QCD激发中表现出来，即核子。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