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

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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.