QUARK-MODEL CALCULATIONS OF CURRENT CORRELATORS IN THE NONPERTURBATIVE DOMAIN

We study the vector-isovector current correlator in this work, making use of a generalized Nambu-Jona-Lasinio (NJL) model. In our work, the original NJL model is extended to describe the coupling of the quark-a ntiquark states to the two-pion continuum. Further, a model for confin ement is introduced that is seen to remove the nonphysical cuts that a ppear in various amplitudes when the quark and antiquark go on mass sh ell. Quite satisfactory results are obtained for the correlator. We al so use the correlator to define a T-matrix for confined quarks and dis cuss a rho-dominance model for that T-matrix. It is also seen that the Bethe-Salpeter equation that determines the rho mass (in the absence of the coupling to the two-pion continuum) has more satisfactory behav ior in the generalized model than in the model without confinement. Th at improved behavior is here related to the absence of the q (q) over bar cut in the basic quark-loop integral of the generalized model. In our model, it is seen how one may work with both quark and hadron degr ees of freedom, with only the hadrons appearing as physical particles. (C) 1995 Academic Press, Inc.