Resonances from meson-meson scattering in U(3) χPT

In this work, the complete one-loop calculation of meson-meson scattering amplitudes within U(3) circle times U(3) chiral perturbation theory with explicit resonance states is carried out for the first time. Partial waves are unitarized from the perturbative calculation employing a nonperturbative approach based on the N/D method. Once experimental data are reproduced in a satisfactory way we then study the resonance properties, such as the pole positions, corresponding residues and their N-C behaviors. The resulting N-C dependence is the first one in the literature that takes into account the fact that the eta(1) becomes the ninth Goldstone boson in the chiral limit for large N-C. Within this scheme the vector resonances studied, rho(770), K*(892) and phi(1020), follow an N-C trajectory in agreement with their standard (q) over barq interpretation. The scalars f(0)(1370), a(0)(1450) and K*(1430) also have for large N-C a (q) over barq pole position trajectory and all of them tend to a bare octet of scalar resonances around 1.4 GeV. The f(0)(980) tends asymptotically to the bare pole position of a singlet scalar resonance around 1 GeV. The sigma, kappa and a(0)(980) scalar resonances have a very different N-C behavior. The case of the sigma resonance is analyzed with special detail.