Phi meson mass and decay width in nuclear matter

The $\phi$ meson spectrum, which in vacuum is dominated by its coupling to the $\bar{K} K$ system, is modified in nuclear matter. Following a model based on chiral SU(3) dynamics we calculate the $\phi$ meson selfenergy in nuclear matter considering the $K$ and $\bar{K}$ in-medium properties. For the latter we use the results of previous calculations which account for $S-$ and $P-$wave kaon-nucleon interactions based on the lowest order meson-baryon chiral effective Lagrangian, and this leads to a dressing of the kaon propagators in the medium. In addition, a set of vertex corrections is evaluated to fulfill gauge invariance, which involves contact couplings of the $\phi$ meson to $S-$wave and $P-$wave kaon-baryon vertices. Within this scheme the mass shift and decay width of the $\phi$ meson in nuclear matter are studied.Comment: 19 pages, 10 figures in EPS format, revtex4; One section modified, some references update

The baryon-decuplet in the chiral dynamics of Lambda-hyperons in nuclear matter

We study the long range part of the $\Lambda$-hyperon optical potential in nuclei using Quantum Many Body techniques and flavor-SU(3) Chiral Lagrangians as starting point. More precisely, we study the contributions to the $\Lambda$-hyperon optical potential due to the long-range two-pion exchange, with $\Sigma$ and $\Sigma^*$ baryons in the internal baryonic lines and considering Nh and $\Delta$h excitations. We also consider the contribution to the spin-orbit potentials that comes out from these terms. Our results support a natural explanation of the smallness of the $\Lambda$-nuclear spin-orbit interaction and shows the importance of the $\Sigma^*$ and $\Delta$ degrees of freedom for the hyperon-nucleus interactions.Comment: 8 pages, 5 figure

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

Two Particle-Hole Excitations in Charged Current Quasielastic Antineutrino--Nucleus Scattering

We evaluate the quasielastic and multinucleon contributions to the antineutrino nucleus scattering cross section and compare our results with the recent MiniBooNE data. We use a local Fermi gas model that includes RPA correlations and gets the multinucleon part from a systematic many body expansion of the $W$ boson selfenergy in the nuclear medium. The same model had been quite successful for the neutrino cross section and contains no new parameters. We have also analysed the relevance of 2p2h events for the antineutrino energy reconstruction.Comment: 6 pages, 4 figure

Neutrino induced coherent pion production

We discuss different parameterizations of the $C_5^A(q^2)$ $N\Delta$ axial form factor, fitted to the old Argonne bubble chamber data for pion production by neutrinos, and we use coherent pion production to test their low $q^2$ behavior. We find moderate effects that will be difficult to observe with the accuracy of present experiments. We also discuss the use of the Rein-Sehgal model for low energy coherent pion production. By comparison to a microscopic calculation, we show the weaknesses of some of the approximations in that model that lead to very large cross sections as well as to the wrong shapes for differential ones. Finally we show that models based on the partial conservation of the axial current hypothesis are not fully reliable for differential cross sections that depend on the angle formed by the pion and the incident neutrino.Comment: Talk given at NUFACT09. 6 latex pages, 7 figures, 1 tabl

New determination of the NN-Δ(1232)\Delta(1232) axial form factors from weak pion production and coherent pion production off nuclei at T2K and MiniBooNE energies revisited

We re-evaluate our model predictions in Phys. Rev. D 79, 013002 (2009) for different observables in neutrino induced coherent pion production. This comes as a result of the new improved fit to old bubble chamber data of the dominant axial C_5^A nucleon-to-Delta form factor. We find an increase of 20%-30% in the values for the total cross sections. Uncertainties induced by the errors in the determination of C_5^A are computed. Our new results turn out to be compatible within about $1\sigma$ with the former ones. We also stress the existing tension between the recent experimental determination of the \sigma(CC coh \pi^+)}/\sigma(NC coh \pi^0)} $ ratio by the SciBooNE Collaboration and the theoretical predictions.Comment: 3 latex pages, 1 figure. Talk given at the NuFact10 Conferenc