The isosinglet unpolarized and isovector polarized twist-2 quark distributions of the nucleon at low normalization point are calculated in the large-N c limit. The nucleon is described as a soliton of the effective chiral theory. We derive the expressions for the distribution functions in the large-N c limit starting from their definition as numbers of partons carrying momentum fraction x in the infinite momentum frame. We develop a numerical method for computation of the quark and antiquark distributions as sums over the quark single-particle levels in the pion field of the soliton. The contributions of the discrete bound-state level as well as the Dirac continuum are taken into account. The quark-and antiquark distributions obtained explicitly satisfy all general requirements. Results are in reasonable agreement with parametrizations of the data at low normalization point.

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At large N c the nucleon can be viewed as a soliton of the effective chiral lagrangian. This picture of nucleons allows a consistent nonperturbative calculation of the leadingtwist parton distributions at a low normalization point. We derive general formulae for the polarized and unpolarized distributions (singlet and non-singlet) in the chiral quark-soliton model. The consistency of our approach is demonstrated by checking the baryon number, isospin and total momentum sum rules, as well as the Bjorken sum rule. We present numerical estimates of the quark and antiquark distributions and find reasonable agreement with parametrizations of the data at a low normalization point. In particular, we obtain a sizeable fraction of antiquarks, in agreement with the phenomenological analysis.

The present review gives a survey of recent developments and applications of the NambuJona-Lasinio model with N f = 2 and N f = 3 quark flavors for the structure of baryons. The model is an effective chiral quark theory which incorporates the SU(N f ) L ⊗SU(N f ) R ⊗U(1) V approximate symmetry of Quantum chromodynamics. The approach describes the spontaneous chiral symmetry breaking and dynamical quark mass generation. Mesons appear as quarkantiquark excitations and baryons arise as non-topological solitons with three valence quarks and a polarized Dirac sea. For the evaluation of the baryon properties the present review concentrates on the non-linear Nambu-Jona-Lasinio model with quark and Goldstone degrees of freedom which is identical to the Chiral quark soliton model obtained from the instanton liquid model of the QCD vacuum. In this non-linear model, a wide variety of observables of baryons of the octet and decuplet is considered. These include, in particular, electromagnetic, axial, pseudoscalar and pion nucleon form factors and the related static properties like magnetic moments, radii and coupling constants of the nucleon as well as the mass splittings and electromagnetic form factors of hyperons. Predictions are given for the strange form factors, the scalar form factor and the tensor charge of the nucleon."Though this be madness, yet there is method in it."Shakespeare, Hamlet, II-2 --