  We perform a complete one-loop calculation of meson-meson scattering, and of
the scalar and pseudoscalar form factors in U(3) chiral perturbation theory
with the inclusion of explicit resonance fields. This effective field theory
takes into account the low-energy effects of the QCD U_A(1) anomaly explicitly
in the dynamics. The calculations are supplied by non-perturbative
unitarization techniques that provide the final results for the meson-meson
scattering partial waves and the scalar form factors considered. We present
thorough analyses on the scattering data, resonance spectroscopy, spectral
functions, Weinberg-like sum rules and semi-local duality. The last two
requirements establish relations between the scalar spectrum with the
pseudoscalar and vector ones, respectively. The Nc extrapolation of the various
quantities is studied as well. The fulfillment of all these non-trivial aspects
of the QCD dynamics by our results gives a strong support to the emerging
picture for the scalar dynamics and its related spectrum.
