J.E. Palomar

Meson exchange in the weak decay of Λ hypernuclei and the Γn/Γp ratio

Abstract We take an approach to the Λ nonmesonic weak decay in nuclei based on the exchange of mesons. 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 ( σ -like exchange), or uncorrelated (box diagrams). Extra effects of ω exchange in the scalar–isoscalar channel are also considered. Constraints of chiral dynamics are used to generate these exchanges. A drastic reduction of the OPE results for the Γ n / Γ 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 good agreement with experiment.

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

We make a theoretical study of the J/psi decays into omegapipi, phipipi, omegaK (K) over bar and phiK (K) over bar 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 phipipi vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered

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

Abstract We study the radiative φ decay into π 0 π 0 γ and π 0 ηγ 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 φ decay into two kaons and then undergo final state interaction leading to the final pair of pions or π 0 η , 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.

Decay of axial vector mesons into VP and P gamma

We propose a phenomenological Lagrangian for the decay of the SU(3) nonets of the axial-vector mesons of J{sup PC}=1{sup +-},1{sup ++} into a vector meson and a pseudoscalar constructed with tensor fields for the vector and axial-vector mesons. The formulation leads to a good reproduction of the different decay branching ratios and assuming vector meson dominance (VMD) it also leads to good results for the radiative decay of the a{sub 1} into pion and photon, and in agreement with the structure proposed in the chiral tensor formulation of radiative decay of axial-vector mesons. The two SU(3) parameters and the mixing angle of K{sub 1A} and K{sub 1B} needed to give the physical K{sub 1}(1270) and K{sub 1}(1400) resonances are also determined.

Chiral loops and VMD in the V→PPγ decays

We evaluate radiative decays of

The φNN coupling from chiral loops

\rho

The ρNN coupling with direct coupling and loops

and

Chiral symmetry and meson exchange approach to hypernuclear decay

\omega

Unitary chiral dynamics in J/Ψ decay into VPP and the role of the scalar mesons

going to two neutral mesons,

New contributions to φ → π0π0γ and φ → π0ηγ decays

\pi^{0} \pi^{0}