Λ(1520)\Lambda(1520) at finite density

We study the decay channels of the $\Lambda(1520)$ in a nuclear medium and find a sizable change - of the order of factor five - of the width of this hyperon at normal nuclear matter density. The mass shift of the $\Lambda(1520)$ is moderate.Comment: Presented at Particles and Nuclei International Conference (PANIC 05), Santa Fe, New Mexico, 24-28 Oct 200

Improved Fixed Center Approximation of the Faddeev equations for the KˉNN\bar{K}NN system with S=0

We extend the Fixed Center Approximation (FCA) to the Faddeev Equations for the $\bar{K} NN$ system with S=0, including the charge exchange mechanisms in the $\bar{K}$ rescattering which have been ignored in former works within the FCA. We obtain similar results to those found before, but the binding is reduced by 6 MeV. At the same time we also evaluate the explicit contribution the $\pi N \Sigma$ intermediate state in the three body system and find that it produces and additional small decrease in the binding of about 3 MeV. The system appears bound by about 35 MeV and the width omitting two body absorption, is about 50 MeV.Comment: 12 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1102.285

AA dependence of the γ\gamma- and pp-induced production of the Λ(1520)\Lambda(1520) from nuclei

Using results of a recent calculation of the $\Lambda(1520)$ in the nuclear medium, which show that the medium width is about five times the free width, we study the A dependence of the $\Lambda(1520)$ production cross section in the reactions $\gamma ~A \to K^+ \Lambda(1520) A^\prime$ and $p~ A \to p~ K^+ \Lambda(1520) A^\prime$. We find a sizable A dependence in the ratio of the nuclear cross sections for heavy nuclei with respect to a light one due to the large value of the $\Lambda(1520)$ width in the medium, showing that devoted experiments, easily within reach in present facilities, can provide good information on that magnitude by measuring the cross sections studied here.Comment: 14 pages, 5 figure

Chiral dynamics in the gamma p --> pi^0 eta p and gamma p --> pi^0 K^0 Sigma^+ reactions

Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ resonance is dynamically generated, we study the reactions $\gamma p \to \pi^0 \eta p$ and $\gamma p \to \pi^0 K^0 \Sigma^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $\Delta^*(1700)$ state which subsequently decays into a pseudoscalar meson and a baryon belonging to the $\Delta(1232)$ decuplet. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $3/2^-$ states. The first reaction is shown to lead to sizable cross sections and the $N^*(1535)$ resonance shape is seen clearly in the $\eta p$ invariant mass distribution. The same dynamical model is shown to lead to much smaller cross sections at low energies in the second reaction. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.Comment: 22 pages, 22 figure

\phi K^{+}K^{-} production in electron-positron annihilation

In this work we study the e^{+}e^{-}\to\phi K^{+}K^{-} reaction. The leading order electromagnetic contributions to this process involve the \gamma*\phi\ K^{+}K^{-} vertex function with a highly virtual photon. We calculate this function at low energies using R\chi PT supplemented with the anomalous term for the VV'P interactions. Tree level contributions involve the kaon form factors and the K*K transition form factors. We improve this result, valid for low photon virtualities, replacing the lowest order terms in the kaon form factors and K*K transition form factors by the form factors as obtained in U\chi PT in the former case and the ones extracted from recent data on e^{+}e^{-}\to KK* in the latter case. We calculate rescattering effects which involve meson-meson amplitudes. The corresponding result is improved using the unitarized meson-meson amplitudes containing the scalar poles instead of the lowest order terms. Using the BABAR value for BR(X\to \phi f_{0})\Gamma (X\to e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good description of data is obtained in the case of destructive interference between this contribution and the previous ones, but more accurate data on the isovector K*K transition form factor is required in order to exclude contributions from an intermediate isovector resonance to e^{+}e^{-}\to \phi\ K^{+}K^{-} around 2.2 GeV.Comment: 21 pages, 17 figures. Revised version to appear in Phys. Rev. D. Contributions of intermediate X(2175) included. Extraction of form factors update

Baryonic Resonances from the Interactions of the Baryon Decuplet and Meson Octet

We study $S$-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons using the lowest order chiral Lagrangian. We find two bound states in the SU(3) limit corresponding to the octet and decuplet representations. These are found to split into eight different trajectories in the complex plane when the SU(3) symmetry is broken gradually. Finally, we are able to provide a reasonable description for a good number of 4-star ${{3/2}}^-$ resonances listed by the Particle Data Group. In particular, the $\Xi(1820)$, the $\Lambda(1520)$ and the $\Sigma(1670)$ states are well reproduced. We predict a few other resonances and also evaluate the couplings of the observed resonances to the various channels from the residues at the poles of the scattering matrix from where partial decay widths into different channels can be evaluated.Comment: Contribution to the HADRON05 Conference, Rio de Janeiro, September 200