Chiral symmetry and meson exchange approach to hypernuclear decay

We take an approach to the $\Lambda$ nonmesonic weak decay in nuclei based on the exchange of mesons under the guidelines of chiral Lagrangians. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange ($\sigma$-like exchange), or uncorrelated (box diagrams). A drastic reduction of the OPE results for the $\Gamma_n/\Gamma_p$ ratio is obtained and the new results are compatible with all present experiments within errors. The absolute rates obtained for different nuclei are also in fair agreement with experiment.Comment: 10 pages, 3 figs. Talk given at the Hypernuclear Conference 2000, Torin

Unitary chiral dynamics in J/ΨJ/\Psi decays into VPPVPP and the role of the scalar mesons

We make a theoretical study of the \J 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\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: Prepared for the 10th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleo

Radiative vector meson decay

We study the radiative $\rho$, $\omega$ and $\phi$ 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. Other mechanisms in which two kaons are produced through the same sequential mechanisms or from vector meson decay into two kaons which undergo final state interaction leading to the final pair of pions or $\pi^0 \eta$, are also considered. The results of the parameter free theory, together with the theoretical uncertainties, are compared with the latest experimental results at Frascati and Novosibirsk.Comment: Prepared for the 10th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleo

Chiral Dynamics of scalar mesons: radiative ϕ\phi decay and σ\sigma in the medium through π0π0\pi^0 \pi^0 nuclear photoproduction

In order to assess the relevance of chiral dynamics in the scalar sector we address two recent problems: radiative decay of the $\phi$, for which there are quite recent data from Frascati, and the modification of the $\sigma$ properties in the nuclear medium seen through the $\pi^0 \pi^0$ photoproduction in nuclei.Comment: Talk given at the High Energy Physics Workshop "Scalar Mesons: an Interesting Puzzle for QCD", Utica, New York, May 200

Isospin dependence of the three-nucleon force

We classify $A$--nucleon forces according to their isospin dependence and discuss the most general isospin structure of the three--nucleon force. We derive the leading and subleading isospin--breaking corrections to the three--nucleon force using the framework of chiral effective field theory.Comment: 21 pages, 6 figure

SMOOTHERS AND THEIR APPLICATIONS IN AUTONOMOUS SYSTEM THEORY

Abstract. In this paper the author introduces the concept of smoother. Roughly speaking, a smoother is a pair (s, K) consisting of a continuous map s sending each point p of its domain into a closed neighborhood Vp of p, and an operator K that transforms any function f into another Kf being smoother than f. This property allows us to remove the effect of a perturbation P from the solutions of an autonomous system the vector field of which is modified by P

Chiral loops and VMD in the V->PPgamma decays

We evaluate radiative decays of $\rho$ and $\omega$ going to two neutral mesons, $\pi^{0} \pi^{0}$ and $\pi^{0} \eta$. We use the sequential vector decay mechanisms in addition to chiral loops and $\rho$-$\omega$ mixing. The chiral loops are obtained using elements of $U\chi PT$ successfully applied in the study of meson-meson interactions up to 1.2 GeV. The chiral loops are found very important in the case of the $\rho \to \pi^{0} \pi^{0} \gamma$ decay and small in the other cases. A good agreement with present measurements of $\rho \to \pi^{0} \pi^{0} \gamma$ and $\omega \to \pi^{0} \pi^{0}\gamma$ is obtained and predictions are made for the other decays where the rates obtained are rather small.Comment: 16 pages, 4 figures. To be published in Nucl. Phys.

Pion and Kaon Vector Form Factors: a Chiral Unitary Approach

The pion and kaon coupled-channel vector form factors are described by making use of the resonance chiral Lagrangian results together with a suitable unitarization method in order to take care of the final state interactions. A very good reproduction of experimental data is accomplished for the vector form factors up to $\sqrt{s}\leq 1.2$ GeV and for the $\pi\pi$ P-wave phase shifts up to $\sqrt{s}\leq 1.5$ GeV.Comment: 4 pages, 2 figures, talk given at MESON 2000, Cracow, Poland, May 19-23, 200

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