In this work, the complete one loop calculation of meson-meson scattering amplitudes within U (3)⊗ 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 non-perturbative 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 η 1 becomes the ninth Goldstone boson in the chiral limit for large N C . Within this scheme the vector resonances studied, ρ(770), K * (892) and φ (1020)

We study meson-baryon scattering with strangeness -1 in unitary chiral perturbation theory. Ten coupled channels are considered in our work, namely, π 0 , π 0 0 , π − + , π + − , K − p,K 0 n, η , η 0 , K 0 0 , and K + − . A large amount of experimental data are analyzed, including the recent precise measurement by the SIDDHARTA Collaboration of the energy shift and width of the 1s state of kaonic hydrogen. This leads to a strong constraint on the free parameters in our theory and of the resulting meson-baryon scattering amplitudes. We also analyze the uncertainty that stems by using several different strategies to perform the fits to data. It is found that large uncertainties in the subthreshold extrapolation of the K − p scattering amplitude arise by either employing only one common weak pseudoscalar decay constant or distinguishing between f π , f K , and f η . However, in both cases a good reproduction of experimental data is obtained. We also discuss the pole content of the resulting S-wave amplitudes, particularly in connection with the two-pole structure of the (1405) resonance.

In this work, we perform the one-loop calculation of the scalar and pseudoscalar form factors in the framework of Uð3Þ chiral perturbation theory with explicit tree level exchanges of resonances. The mesonmeson scattering calculation from Guo and Oller [Phys. Rev. D 84, 034005 (2011)] is extended as well. The spectral functions of the nonet scalar-scalar (SS) and pseudoscalar-pseudoscalar (PP) correlators are constructed by using the corresponding form factors. After fitting the unknown parameters to the scattering data, we discuss the resonance content of the resulting scattering amplitudes. We also study spectral-function sum rules in the SS À SS, PP À PP, and SS À PP sectors as well as semilocal duality from scattering. The former relate the scalar and pseudoscalar spectra between themselves while the latter mainly connects the scalar spectrum with the vector one. Finally we investigate these items as a function of N C for N C > 3. All these results pose strong constraints on the scalar dynamics and spectroscopy that are discussed. They are successfully fulfilled by our meson-meson scattering amplitudes and spectral functions.