Large N_c behavior of light resonances in meson-meson scattering

By scaling the parameters of meson-meson unitarized Chiral Perturbation Theory amplitudes according to the QCD large N_c rules, one can study the spectroscopic nature of light meson resonances. The scalars sigma, kappa f_0(980) and, possibly, the a_0(980) do not seem to behave as q-qbar states, in contrast to the vectors rho(770) and K*(892). The behavior shown by the scalars is naturally explained in terms of diagrams with intermediate $\bar q\bar q qq$-like states. Here we review our recent study and show how the results do not depend on the different fits to data.Comment: 6 pages. To appear in the proceedings of the HADRON03 conference, Aschaffenburg, Germany. September 200

Dispersive chiral approach to Meson-meson dynamics: Spectroscopy results for light scalars and precision studies

Dispersive approaches provide model independent description of meson-meson scattering. We first review here the use of dispersion relations to obtain a model independent unitarization of Chiral Perturbation Theory amplitudes, that establish the existence of light scalar mesons and whose leading 1/N_c behavior suggest they ahve a non q-qbar dominant component. We also review the forward dispersion relation checks on conflicting experimental data and the resulting very precise pion-pion scattering scattering amplitudes.Comment: 8 pages. Invited Plenary talk at the Conference ``Quark Confinement and the Hadron SpectrumVII''. 2-7th Sept. 2006. Ponta Delgada, Azores Islands. Portuga

Poles of light resonances from unitarized Chiral perturbation Theory and their large Nc behavior

We have recently completed the one loop calculation of meson-meson scattering within Chiral Perturbation Theory. Once unitarized, these amplitudes provide simultaneously a remarkable description of the resonance region up to 1.2 GeV as well as the low energy region, respecting the chiral symmetry expansion. The position of the poles in these amplitudes is related to the mass and width of the associated resonances that are generated without being explicitly included in the Lagrangian. The spectroscopic nature of these states can then be deduced by studying the behavior of these poles, through the Nc dependence of the Chiral Perturbation Theory parameters, which can be obtained from QCD in the large Nc limit.Comment: Invited talk to the 25th MRST, Conference on High Energy Physics (``J. Schechter Fest''). May 13 - 15, 2003, Syracuse University, Syracuse, New York. 13 pages, 2 figure

Consistency checks of different pion-pion scattering data sets using forward dispersion relations

We review our evaluation of forward dispersion relations for direct fits to the different, and often conflicting, pion-pion scattering experimental analyses. We find that some of the most commonly used data sets do not satisfy these constraints by several standard deviations. We also provide a consistent pion-pion amplitude by improving a global fit to data with these dispersion relations.Comment: To appear in the Proceedings of the XI. International Conference on Hadron Spectroscopy- HADRON05. Rio de Janeiro. 21st-25th August. 200