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We demonstrate the equivalence of the light-front, equal-time and covariant formulations in meson-baryon interactions. In particular, we discuss the self-energy Σ of a nucleon dressed by pion loops with the pseudovector πNN coupling. It is shown that the leading nonanalytic behavior of Σ is equivalent whichever formulations are used for the derivation. [ABSTRACT FROM AUTHOR]

A combined analysis of new π0 and η photoproduction data from CB-ELSA collaboration was performed including the earlier data from SAID data base, new data on beam asymmetry from the GRAAL collaboration and data on γp → KΛ and KΣ. Three baryon resonances have a substantial coupling to ηN, the well known N(1535)S11, N(1720)P13 and the newly observed N(2070)D15 resonance. A new P11 state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data also demand the presence of two D13 states at 1870 and 2170 MeV. The properties of observed states and their contributions to different observables are discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We study the Λ(1520) resonance in a coupled channel approach involving the πΣ(1385), K[cap_xi](1530), KN and πΣ channels. Implementing unitarity in coupled channels, we make an analysis of the relative importance of the different mechanisms which contribute to the dynamical structure of this resonance. From experimental information on some partial wave amplitudes and constraints imposed by unitarity, we get a comprehensive description of the amplitudes and hence the couplings to the different channels. We test these amplitudes in different reactions like K-p → Λππ, γp → K+K-p, γp → K+π0π0Λ and π-p → K0K-p and find a fair agreement with the experimental data. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The K-p → π0π0Σ0 reaction is studied within a chiral unitary model. The distribution of π0Σ0 states forming the Λ(1405) shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of Γ = 38 MeV. We use these data in combination with those of the π-p → K0πΣ reaction and elements of chiral unitary theory to prove that there are two Λ(1405) states instead of one as so far assumed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A program to measure the two-pion production in nucleon-nucleon collisions exclusively and in all channels from threshold up to Tp = 1360 MeV has been started at CELSIUS-WASA. First preliminary results for ppπ+π¯ and ppπ0π0 channels are presented. In the near-threshold region they are consistent with a dominance of the Roper excitation and its successive decay into Nσ and Δπ channels. At energies Tp > 1 GeV we observe a very different behavior, which is at variance with theoretical predictions. At COSY-TOF exclusive measurements of the pp → ppπ+π¯ reaction have been carried out with polarized beam. Preliminary results show non-zero analyzing powers which point to a sizeable admixture of l ≠ 0 partial waves indicating possibly an influence of the ρ-channel. [ABSTRACT FROM AUTHOR]