We make a theoretical study of the s-wave interaction of the nonet of vector mesons with the octet of pseudoscalar mesons starting from a chiral invariant Lagrangian and implementing unitarity in coupled channels. By looking for poles in the unphysical Riemann sheets of the unitarized scattering amplitudes, we get two octets and one singlet of axial-vector dynamically generated resonances. The poles found can be associated to most of the low lying axial-vector resonances quoted in the Particle Data Book: b 1 (1235), h 1 (1170), h 1 (1380), a 1 (1260), f 1 (1285) and two poles to the K 1 (1270) resonance. We evaluate the couplings of the resonances to the V P states and the partial decay widths in order to reinforce the arguments in the discussion.

We perform a theoretical analysis of the Λ b → J/ψK − p reaction from where a recent LHCb experiment extracts a Λ(1405) contribution in the K − p spectrum close to threshold and two baryon states of hidden charm in the J/ψ p spectrum. We recall that baryon states of this type have been theoretically predicted matching the mass, width and J P of the experiment, concretely some states built up from the J/ψ N ,D * Λc,D * Σc,DΣ * c andD * Σ * c coupled channels. We assume that the observed narrow state around 4450 MeV has this nature and we are able to describe simultaneously the shapes and relative strength of the the K − p mass distribution close to threshold and the peak of the J/ψ p distribution, with values of the J/ψ p coupling to the resonance in line with the theoretical ones. The non trivial matching of many properties gives support to a J P = 3/2 − assignment to this state and to its nature as a molecular state mostly made ofD * Σc andD * Σ * c .PACS numbers:

The axial vector meson K1(1270) was studied within the chiral unitary approach, where it was shown that it has a two-pole structure. We reanalyze the high-statistics WA3 experiment K − p → K − π + π − p at 63 GeV, which established the existence of both K1(1270) and K1(1400), and we show that it clearly favors our two-pole interpretation. We also reanalyze the traditional K-matrix interpretation of the WA3 data and find that the good fit of the data obtained there comes from large cancellations of terms of unclear physical interpretation.

The radiative decay of the axial-vector resonances into a pseudoscalar meson and a photon is studied using the vector meson Lagrangian obtained from the hidden gauge symmetry (HGS) formalism. The formalism is well suited to study this problem since it deals with pseudoscalar and vector mesons in a unified way, respecting chiral invariance. We show explicitly the gauge invariance of the set of diagrams that appear in the approach and evaluate the radiative decay width of the a1(1260) and b1(1235) axial vector meson resonances into pi gamma. We also include the contribution of loops involving anomalous couplings and compare the results to those obtained previously within another formalism.Comment: 24 pages, 6 tables, 11 figure

We make a theoretical study of the J/Ψ decays into ωππ, φππ, ωKK and φKK 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/Ψφππ vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered.

Recently we presented a successful strategy to extract the position of the two (1405) poles from experimental photoproduction data on the γp → K + π 0 0 reaction at Jefferson Lab. Following a similar strategy, we extend the previous method to incorporate also the isospin 1 component which allows us to consider in addition the experimental data on γp → K + π ± ∓ . The idea is based on considering a production mechanism as model independent as possible and implementing the final state interaction of the final meson-baryon pair based on small modifications of the unitary chiral perturbation theory amplitudes. Good fits to the data are obtained with this procedure, by means of which we can also predict the cross sections for the K − p →KN, π , and π reactions for the different charge channels. Besides the two poles found for the (1405) resonance, we discuss the possible existence of an isospin 1 resonance in the vicinity of theKN threshold.

We make a theoretical study of the charge and forward-backward pion asymmetries in the e + e − → π + π − γ process on and off the φ resonance energy. These observables are rather sensitive to the inner details of the theoretical models to describe the reaction. In addition to the standard implementation of the initial state radiation (ISR) and the Bremsstrahlung contribution to the final state radiation (FSR), we use the techniques of the chiral unitary approach to evaluate the contribution from the mechanisms of φ decay into π + π − γ. This contribution involves the implementation of final state interaction from direct chiral loops, the exchange of vector and axial-vector resonances and the final state interaction through the consideration of the meson-meson unitarized amplitudes, which where found important in a previous work describing the φ → ππγ. We find a good reproduction of the experimental data from KLOE for the forward-backward asymmetry, both at the φ peak and away from it. We also make predictions for the angular distributions of the charge asymmetry and show that this observable is very sensitive to the chiral loops involved in φ radiative decay.PACS numbers:

Recent information on invariant mass distributions of the γp → π + π 0 n reaction, where previous theoretical models had shown deficiencies, have made more evident the need for new mechanisms, so far neglected or inaccurately included. We have updated a previous model to include new necessary mechanisms. We find that the production of the ρ meson, and the ∆(1700) excitation, through interference with the dominant terms, are important mechanisms that solve the puzzle of the γp → π + π 0 n reaction without spoiling the early agreement with the γp → π + π − p and γp → π 0 π 0 p reactions.