Origin of resonances in the chiral unitary approach

Abstract

We study the origin of the resonances associated with pole singularities of the scattering amplitude in the chiral unitary approach. We propose a ``natural renormalization'' scheme using the low-energy interaction and the general principle of the scattering theory. We develop a method to distinguish dynamically generated resonances from genuine quark states [Castillejo-Dalitz-Dyson (CDD) poles] using the natural renormalization scheme and phenomenological fitting. Analyzing physical meson-baryon scatterings, we find that the $\ensuremath{\Lambda}(1405)$ resonance is largely dominated by the meson-baryon molecule component. In contrast, the $N(1535)$ resonance requires a sizable CDD pole contribution, while the effect of the meson-baryon dynamics is also important.