Confinement and the composite 'pionic' Goldstone mode via the NJL mechanism in a bag-like potential model

We start from an effective lagrangian for massless u- and d-quarks containing a chiral-symmetric effective interaction with a position-dependent coupling strength. We study the appearance of the pseudoscalar isovector Goldstone mode, which is generated by the spontaneous breakdown of chiral symmetry due to the selfconsistent confining potential. The introduction of small current quark masses (proportional8 MeV) leads to a finite energy eigenvalue of proportional140 MeV. The ''wave function'' of the mode is determined up to a normalization by the single-quark propagator and depends strongly on the cutoff parameter. We compare it with that of a single qanti q ''bag'' state. (orig.)