Resonances, Chiral Symmetry, Coupled Channel Unitarity and Effective Lagrangians

By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in meson-meson scattering up to 1.2 GeV using the parameters of the O(p^2) and O(p^4) Chiral Lagrangian. We report on an update of these results examining their possible relevance for meson spectroscopy.Comment: To appear in the proceedings of the 8th International Conference on Hadron Spectroscopy, HADROn 99, August 24-28, 1999, Beijing, China. Four pages, uses espcrc1.sty (included

Finite width effects in \phi radiative decays

The decay widths \phi \to \gamma f_0(980) and \phi \to \gamma a_0(980) are calculated taking into account the finite widths of the scalar resonances f_0(980) and a_0(980). The latter are shown to be essential in order to obtain meaningful results. Simultaneously we also study the decays \phi\to \gamma \pi^0\pi^0 and \gamma \pi^0\eta where a good reproduction of the recent experimental data is obtained, pointing out the necessity of a \phi\gamma K^0\bar{K}^0 contact vertex. The calculated decay rates to \gamma f_0(980) and \gamma a_0(980) are in good agreement with the experimental ones without invoking isospin breaking in the couplings of the f_0(980) and a_0(980) resonances to the K^+ K^- and K^0 \bar{K}^0 channels, at odds with recent proposals. The derived formula for calculating these \phi radiative decay widths can be also applied in their own experimental analyses in order to obtain more precise results.Comment: 20 pages, 6 figures. One reference is corrected. Version to be published in Nuclear Physics

Sequential vector and axial-vector meson exchange and chiral loops in radiative phi decay

We study the radiative $\phi$ decay into $\pi^0 \pi^0 \gamma$ and $\pi^0 \eta \gamma$ taking into account mechanisms in which there are two sequential vector-vector-pseudoscalar or axial-vector--vector--pseudoscalar steps followed by the coupling of a vector meson to the photon, considering the final state interaction of the two mesons. There are other mechanisms in which two kaons are produced through the same sequential mechanisms or from $\phi$ decay into two kaons and then undergo final state interaction leading to the final pair of pions or $\pi^0 \eta$, this latter mechanism being the leading one. The results of the parameter free theory, together with the theoretical uncertainties, are compared with the latest experimental results of KLOE at Frascati.Comment: 28 pages, 20 figure

Aspects of Strangeness -1 Meson-Baryon Scattering

We consider meson-baryon interactions in S-wave with strangeness -1. This is a sector populated by plenty of resonances interacting in several two-body coupled channels. We consider a large set of experimental data, where the recent experiments are remarkably accurate. This requires a sound theoretical description to account for all the data and we employ Unitary Chiral Perturbation Theory up to and including O(p^2). The spectroscopy of our solutions is studied within this approach, discussing the rise from the pole content of two \Lambda(1405) resonances and of the \Lambda(1670), \Lambda(1800), \Sigma(1480), \Sigma(1620) and \Sigma(1750). We finally argue about our preferred fit.Comment: 6 figures, 3 figures, talk given in the IVth International Conference on Quarks and Nuclear Physics (QNP06), Madrid June 5th and 10th, 2006. One reference is update

Description of the Ds∗(2320)D^*_s(2320) resonance as the DπD\pi atom

We discuss the possibility that the recently reported resonance in the $D_s \pi^0$ spectrum can be described in terms of residual $D\pi$ interactions.Comment: 3 pages, 1 figur

Unitary chiral dynamics in J/Psi to VPP decays and the role of scalar mesons

We make a theoretical study of the J/Psi decays into \omega\pi\pi, \phi\pi\pi, \omega K \bar{K} and \phi K\bar{K} using the techniques of the chiral unitary approach stressing the important role of the scalar resonances dynamically generated through the final state interaction of the two pseudoscalar mesons. We also discuss the importance of new mechanisms with intermediate exchange of vector and axial-vector mesons and the role played by the OZI rule in the J/\Psi\phi\pi\pi vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.Comment: 29 pages, 10 figure

Dynamical Generation of Hyperon Resonances

In this talk we report on how, using a chiral unitary approach for the meson--baryon interactions, two octets of $J^{\pi}=1/2^-$ baryon states and a singlet are generated dynamically, resulting in the case of strangeness $S=-1$ in two poles of the scattering matrix close to the nominal $\Lambda(1405)$ resonance. We suggest experiments which could show evidence for the existence of these states.Comment: Invited talk in the VIII International Conference on Hypernuclei and Strange Particle Physic

Pole structure and compositeness

We present in this talk a series of new results on the nature of a bound state or resonance based on the calculation of the expectation values of the number operators of the free particles in the state of interest. In this way, a new universal criterion for the elementariness of a bound state emerges. In the case of large particle wavelengths compared to the range of their interaction, a new closed formula for the compositeness of a bound state in a two-particle continuum is obtained. The extension of these results to resonances with respect to the open channels can be given by making use in addition of suitable phase-factor transformations as also reviewed here. We end with a discussion on the $X(3872)$ as possible double- or triple-pole virtual state, which would be the first case in particle phenomenology.Comment: 10 pages, 4 figures. Plenary talk at Hadron201

Nucleon-Nucleon Interactions from Effective Field Theory

We have established a new convergent scheme to treat analytically nucleon-nucleon interactions from a chiral effective field theory. The Kaplan-Savage-Wise (KSW) amplitudes are resummed to fulfill the unitarity or right hand cut to all orders below pion production threshold. This is achieved by matching order by order in the KSW power counting the general expression of a partial wave with resummed unitarity cut, with the inverses of the KSW amplitudes. As a result, a new convergent and systematic KSW expansion is derived for an on-shell interacting kernel \cR in terms of which the partial waves are computed. The agreement with data for the S-waves is fairly good up to laboratory energies around 350 MeV and clearly improves and reestablishes the phenomenological success of the KSW amplitudes when treated within this scheme.Comment: 30 pages, 8 figures, enlarged and more detailed version, new results, version to be published in Nucl. Phys.