We improve the calculations of the η → π 0 γγ decay within the context of me-son chiral lagrangians. We use a chiral unitary approach for the meson-meson interaction, thus generating the a 0 (980) resonance and fixing the longstanding sign ambiguity on its contribution. This also allows us to calculate the loops with one vector meson exchange, thus removing a former source of uncertainty. In ad...

We study the vector and scalar meson-meson amplitudes up to √ s . 1.4 GeV and their associated spectroscopy. The study has been done considering jointly the N/D method, Chiral Symmetry and implications from large Nc QCD [1]. The N/D method provides us with the way to unitarize the tree level amplitudes constructed in agreement with Chiral Symmetry and its breaking (explicit and spontaneous). Th...

We present model independent constraints on the masses and couplings to fermions of B and L conserving leptoquarks. Such vector or scalar particles could have masses below 100 GeV and be produced at HERA; we list the generation dependent bounds that can be calculated from rare lepton and meson decays, meson-anti-meson mixing and various electroweak tests.

We report on progress in the development of a microscopic model for the hyperon-nucleon interaction within the meson-exchange framework, which incorporates both one-meson as well as correlated two-meson exchange contributions. The main new feature of the model is the exchange of two correlated pions or kaons, both in the scalar-isoscalar and the vector-isovector channels. In the scalar channel ...

We have calculated the D-meson spectral density at finite temperature within a self-consistent coupled-channel approach that generates dynamically the Λ c (2593) resonance. We find a small mass shift for the D-meson in this hot and dense medium while the spectral density develops a sizeable width. The reduced attraction felt by the D-meson in hot and dense matter together with the large width o...

We calculate the effective mass m∗ω of the ω-meson in nuclear medium by the σ-ω model with a vector field self-interaction (VFSI). We found that the direct and the indirect effects of the VFSI almost cancel each other and the result is changed only slightly at the normal density. The VFSI makes m∗ω smaller at lower density and makes m ∗ ω larger at higher density. However, both effects are not ...

The cross sections for J/c absorption by p and r mesons are studied in a meson-exchange model that includes not only pseudoscalar-pseudoscalar-vector-meson couplings but also three-vector-meson and fourpoint couplings. We find that they are much larger than in a previous study where only pseudoscalarpseudoscalar-vector-meson couplings were considered. Including form factors at interaction verti...

We present the general formalism required to derive generalized parton distributions within a convolution model where the bare nucleon is dressed by its virtual meson cloud. In the one-meson approximation the Fock states of the physical nucleon are expanded in a series involving a bare nucleon and two-particle, meson-baryon, states. The baryon is assumed here to be either a nucleon or a ∆ descr...