On the scalar nonet in the extended Nambu–Jona-Lasinio model

We discuss the lightest scalar resonances, f0(600), κ(800), a0(980) and f0(980) in the extended Nambu–Jona-Lasinio model. We find that the model parameters can be tuned, but unnaturally, to accommodate those scalars except the f0(980). We also discuss problems encountered in the K-matrix unitarization approximation by using Nc counting technique.