The Light and Heavy Scalars in Unitarized Coupled Channel and Lagrangian Approaches

Using ideas underlying the flavour-blind "Nijmegen Unitarised Meson Model" we try to understand on the basis of a system of Schroedinger equations with one meson-meson and one (spinless) quark-antiquark channel coupled by a simple delta-shell transition potential the formation of (e.g. scalar) meson-meson scattering singularities in the complex momentum and energy plane. Surprisingly we are able to describe without direct meson-meson interaction and without any need for glueballs the whole known scalar meson spectrum. "Light" scalar mesons (e.g. f0(600), kappa(800), f0(980), a0(985), D*0(2290), ...) are identified to belong to the spectrum of the transition potential, while "heavy" scalars (e.g. f0(1370), K*0(1430), f0(1500), f0(1710), a0(1450), D*0(2621) (?), D*0(2825) (?), D*sJ(2928) (?), ...) are related to the confinement spectrum. Due to the particular value of the charm-strange reduced quark mass level-(anti)crossing in the complex momentum plane occurs which relates the BABAR state Ds(2317) to the bare groundstate of the confinement spectrum, while the respective groundstate of the transition potential ends up as D*sJ(2782) (?). We conclude with a short comment on (our) recent progress in the consistent quantum field theoretical effective description of resonances within a Lagrangian framework.