Dynamical Generation of Scalar Mesons
  Starting with just one bare seed for each member of a scalar nonet, we investigate when it is possible to generate more than one hadronic state for each set of quantum numbers. In the framework of a simple model, we find that in the I=1 sector it is possible to generate two physical states with the right features to be identified with the a_0(980) and the a_0(1450). In the I=1/2 sector, we can generate a number of physical states with masses higher than 1 GeV, including one with the right features to be associated with the K_0^*(1470), but none which can be identified with the light kappa scalar meson. The I=0 sector is the most complicated and elusive: since all outcomes are very strongly model dependent, we cannot draw any robust conclusion. Nevertheless, we find that in that case too, depending on the coupling scheme adopted, the occurrence of numerous states can be achieved. This shows that dynamical generation of physical states is a possible solution to the problem of accounting for more scalar mesons than can fit in a single nonet, as experiments clearly deliver. 
M. Boglione and M.R. Pennington