Quark-antiquark resonances in the NJL model

Abstract

The problem of the $\rho$ meson resonance solution in the extended NJL model is studied. It has been shown previously that the solution for the $\rho$ meson changes smoothly from a bound state to a "virtual state" when the vector channel attraction becomes too weak to support bound state solutions. We have found that together with these solutions a separate resonance branch appears which is not connected smoothly with the bound state solutions. At small values of constituent quark mass, $m\sim 200$ MeV, it corresponds to the physical vector meson resonance solution in the quark-continuum region. The $a_1$ and $\sigma$ resonances are also discussed.