arXiv subjects
Publications and source records attributed to J. E. Palomar.
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.
We study the radiative $ρ$, $ω$ and $ϕ$ 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. 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 $π^0 η$, 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.
We make a theoretical study of the $\J$ decays into $ωππ$, $ϕππ$, $ωK \bar{K}$ and $ϕK\bar{K}$ 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 $\Jϕππ$ vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.
We propose a phenomenological Lagrangian for the decay of the SU(3) nonets of the axial-vector mesons of $J^{PC}=1^{+-},1^{++}$ 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 $a_1$ 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 $K_{1A}$ and $K_{1B}$ needed to give the physical $K_1(1270)$ and $K_1(1400)$ resonances are also determined.
We make a theoretical study of the J/Psi decays into ωππ, ϕππ, ωK \bar{K} and ϕK\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/Ψϕππvertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.
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.
Starting from a gauge formalism of $ρ$ mesons, pions and baryons we evaluate the $ρ$ coupling to the nucleon, including the direct coupling provided by the Lagrangians, plus contributions from loops with the virtual pion cloud. We find a contribution to the magnetic $ρ$ coupling to the nucleon from pionic loops of the same size as the direct coupling, which is, however, still small compared to the empirical values. This finding goes in line with chiral formulations of the strong interaction of mesons at low energies where, unlike the scalar mesons which are mostly built of a pion (kaon) cloud, the $ρ$ meson stands as a genuine QCD state with intrinsic properties not tied to those of the pion cloud.
Starting from effective Lagrangians which combine a gauge formulation of Vector Meson Dominance with Chiral Lagrangians, the coupling of the phi to the nucleon, which is zero at tree level due to the OZI rule, is calculated perturbatively considering loop contributions to the electric and magnetic form factors. We obtain reasonably smaller values for both form factors than those for rho NN and consistent with the expected order of magnitude of the OZI rule violation.
We evaluate radiative decays of $ρ$ and $ω$ going to two neutral mesons, $π^{0} π^{0}$ and $π^{0} η$. We use the sequential vector decay mechanisms in addition to chiral loops and $ρ$-$ω$ mixing. The chiral loops are obtained using elements of $UχPT$ 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 $ρ\to π^{0} π^{0} γ$ decay and small in the other cases. A good agreement with present measurements of $ρ\to π^{0} π^{0} γ$ and $ω\to π^{0} π^{0}γ$ is obtained and predictions are made for the other decays where the rates obtained are rather small.
We make use of recent accurate results obtained for the pion and kaon vector form factors within a chiral unitary approach in order to calculate the decay widths of the $τ$ lepton to these mesons and also to evaluate the contribution of this two mesons to the anomalous magnetic moment of the muon, the running of the fine structure constant and the muonium hyperfine splitting.
We take an approach to the Lambda non-mesonic 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 (sigma-like exchange), or uncorrelated (box diagrams). Extra effects of omega 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 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 good agreement with experiment.
We develop a unitarity approach to consider the final state interaction corrections to the tree level graphs calculated from Chiral Perturbation Theory ($χPT$) allowing the inclusion of explicit resonance fields. The method is discussed considering the coupled channel pion and kaon vector form factors. These form factors are then matched with the one loop $χPT$ results. A very good description of experimental data is accomplished for the vector form factors and for the $ππ$ P-wave phase shifts up to $\sqrt{s}\lesssim 1.2$ GeV, beyond which multiparticle states play a non negligible role. In particular the low and resonance energy regions are discussed in detail and for the former a comparison with one and two loop $χPT$ is made showing a remarkable coincidence with the two loop $χPT$ results.
We take an approach to the $Λ$ 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 ($σ$-like exchange), or uncorrelated (box diagrams). 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 fair agreement with experiment.
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 $ππ$ P-wave phase shifts up to $\sqrt{s}\leq 1.5$ GeV.