A Study of Nucleon Structure based on the Chiral Quark Soliton Model

手征夸克孤子模型（CQSM）无疑是最简单的重子模型，它包含了低能QCD的基本特征，即：e.手征对称性及其自发破缺。我们研究这个模型的一个主要动机是理解Skyrme模型的基本动力学意义，在Skyrme模型中，核子（费米子）是由π场（玻色子）构成的。由于Skyrme模型中的经典π介子场位形与CQSM中夸克的平均场势之间存在着有趣的对应关系，我们成功地阐明了Skyrme模型的微观基础。这并不意味着这两个模型是完全等价的。我们已经表明，对于一个合理的选择模型参数，CQSM是更现实的比Skyrme模型在许多方面。从实用的观点看，CQSM最显著的特点之一是它使我们能够在完全包含Dirac-sea夸克自由度的情况下求解核子束缚态问题，我们发现核子内部的qq海是同位旋不对称的，这与最近NMC对核子结构函数的分析完全一致。根据我们的非微扰分析，核子内qq海的这种同位旋不对称性是手征对称性自发破缺的必然结果，同时核子内价夸克数也必然存在味不对称性。这就打破了微扰QCD的普遍教条，即核子中的qq海不携带味量子数。

The chiral quark soliton model (CQSM) is undoubtedly the simplest model of baryons, which incorporates the basic feature of the low energy QCD, i. e. the chiral symmetry and its spontaneous breaking. A main motivation of our study of this model is to understand the underlying dynamical meaning of the Skyrme model in which the nucleon (a fermion) is constructed from the pion fields (bosons). Taking care of the interesting correspondence between the classical pion field configuration in the Skyrme model and the mean-field potential for quarks in the CQSM, we have succeeded to clarify the microscopic foundation of the Skyrme model. This hoewever does not mean that these two models are completely equivalent. We have rather shown that, for a reasonable choice of the model parameters, the CQSM is more realistic than the Skyrme model in many respects. From the practical viewpoint, one of the most prominant features of the CQSM is that it enables us to solve the nucleon bound state problem with full inclusion of the Dirac-sea quark degrees of freedom in addition to the N_c valence quarks in it. We have found that the qq sea inside the nucleon is isospin asymmetric in completely consistent with the recent NMC analysis of the nucleon structure functions. According to our nonperturbative analysis, this isospin asymmetry of the qq sea inside the nucleon is an inevitable consequence of the spontaneous chiral symmetry breaking, combined with the flavor asymmetry certainly existing in the valence quark numbers in the nucleon. This then breaks down the widespread dogma of the perturbative QCD that the qq sea in the nucleon carries no flavor quantum numbers.