The Strange Content of the Baryons in the Su(3)-Nambu-Jona-Lasinio Model

Abstract

Today Quantum Chromodynamics (QCD) is assumed to be the theory of the strong interactions. Nevertheless it could be proved only in the high energy regime thanks to the celebrated asymptotic freedom¹. For the static properties of the mesons and baryons, which are described by the rather low energy features of QCD, up to now only the calculations on a lattice could give some crude estimates^2,3. Therefore one was faced with developing some effective theories, which incorporate the relevant properties. These are chiral symmetry and the spontaneous breaking of this symmetry, which leads to the appearance of the so called Goldstone bosons. Within the SU(3)-flavor symmetry, which is in the present approach believed to be still a good symmetry of the strong interactions, these massless bosons are the pions, the kaons and the eta particle. Because in nature there are no massless mesons, one can give them a small mass via the introduction of small current quark masses. Besides the older Skyrme model⁴, which mimics these features by purely mesonic degrees of freedom, and the Gell-Mann Lévi model⁵, which contains in addition also valence quarks, there are above all the chiral quark model of Dyakonov and Petrov⁶ and the NambuJona-Lasinio (NJL) model ⁷. One should stress however that the latter ones are not only phenomenological models but can be viewed as some realistic long-wavelength expansion of QCD^6–12. In these models the chiral symmetry is broken dynamically by the inclusion of the one-fermion loop contribution to the effective potential. These loop contributions represent in the solitonic sector of the theory theolarization of the whole Dirac sea due to the presence of the N _c valence quarks^13–17.