We examine flavor SU(3) breaking effects on meson-baryon scattering amplitudes in the chiral unitary model. It turns out that the SU(3) breaking, which appears in the leading quark mass term in the chiral expansion, can not explain the channel dependence of the subtraction parameters of the model, which are crucial to reproduce the observed scattering amplitudes and resonance properties.PACS numbers: 12.39. Fe, 11.80.Gw, 14.20.Gk, 14.20.Jn, 11.30.Hv Keywords: chiral unitary approach, meson-baryon scatterings, flavor SU(3) breaking Properties of baryonic excited states are investigated with great interest both theoretically and experimentally. Recently, the chiral unitary model has been successfully applied to this problem, especially to the first excited states of negative parity (J P = 1/2 − ) such as Λ(1405) and N (1535) [1,2,3,4,5,6,7]. In this method, based on the leading order interactions of the chiral Lagrangian and the unitarization of the S-matrix, the baryon resonances are dynamically generated as quasi-bound states of ground state mesons and baryons. It reveals the importance of chiral dynamics not only in the threshold but also in the resonance energy region.In the chiral unitary model for the meson-baryon scattering, we consider the coupled channel scatterings of the octet mesons and baryons. Imposing the unitarity condition on the scattering amplitudes T ij in the N/D method, we obtain the scattering equation in the matrix form Refs. [3,8]:where V ij denotes the elementary tree level interaction derived from the chiral Lagrangian. This equation can be solved algebraically. The loop integral G i is the fundamental building block in the chiral unitary model and are regularized by the dimensional regularization;with Ln ±± ≡ ln(±s ± (M 2 i − m 2 i ) + 2 √ sq i )), the masses of baryon and meson M i and m i , the three-momentum of the mesonq i , the total energy in the center of mass system

We investigate Λ(1520, 3/2 − , D 03 ) photoproduction via the γN → KΛ * process. Using effective Lagrangians, we compute the total and differential cross sections. The dependence on the momentum transfer for the photoproduction at the tree-level is also examined. We find that the total cross sections for the proton target are well reproduced as compared with the experimental data. It turns out that the total cross sections for the neutron target are significantly smaller than those for the proton one. We also compare the present results with the γN →KΘ + reaction in order to extract information of Θ + . The role of K * -exchange in the production reaction is also discussed.Recent interest in excited baryons has been largely motivated by new experimental developments [1]: The observation of the exotic Θ + resonance of strangeness S = +1 has triggered diverse activities in both experimental and theoretical studies. The finding of the Θ + has renewed interest in baryon spectroscopy. For instance, properties of the Λ(1405) has been reanalyzed, based on the idea of chiral perturbation theory and of dynamical generation from (anti) kaon-nucleon scattering. A meson-baryon bound-state picture suggests another type of the multi-quark structure. A spin-3/2 − partner of this resonance, i.e. Λ(1520) (≡ Λ * ) whose mass is similar to that of Θ + but strangeness is opposite is yet another interesting resonance. It can be produced simultaneously in the Θ + photoproduction from the deuteron target. The LEPS collaboration is searching for the Θ + associated with the production of the Λ * in photoproduction off the deuteron [2]. Since the measurement of the Λ * can be performed much more reliably, the detailed understanding of the production mechanism of this resonance would be useful to extract information of the Θ + .As far as the experimental data of the Λ * production are concerned, there are experiments reported so far: Boyarski (photoproduction)et al. [3], the Daresbury group (photoproduction) [4], and the CLAS collaboration (electroproduction) [5]. However, these two production mechanisms showed rather different tendencies: While in Ref.[3] and in the Daresbury experiment K * -exchange is known to be dominant in the t-channel, the CLAS experiment indicates that pseudoscalar K-exchange governs the process. Moreover, the kinematical regions of these experiments are different, so that a mere comparison is not meaningful.In the present work, we investigate the photoproduction of the Λ * near the threshold. Based on the effective Lagrangian for meson-baryon vertices, we use the Born approximation. We introduce form factors at the vertices, which reflect the internal structure of hadrons but bring in model dependence. However, there is a caveat: Introducing the form factors violates the gauge invariance of the electromagnetic interaction, which causes the Ward-Takahashi identity to be broken. Thus, we have to take care of the form factors to restore the gauge invariance. Since there is no unique theoretical way to introduce the g...

We investigate the Λ(1520, 3/2 − ) ≡ Λ * photoproduction off the proton target beyond the resonance region within a model including the Regge contributions, the tree-level diagrams with the nucleon and the certain resonance intermediate states and one contact term. The Reggeized propagators for the K and K * exchanges in the t channel are employed in a gauge-invariant manner. We compute the angular and energy dependences of the cross section and some polarization observables, such as the photon-beam asymmetry and the polarization-transfer coefficients. Our results qualitatively agree with the current experimental data. We find that the Regge contributions are necessary to explain the high-energy data beyond Eγ ≈ 4 GeV, especially for the angular dependences in the forward region. On the contrary, the polarization observables are insensitive to the Regge contributions due to the contact-term dominance which is a consequence of gauge invariance. We also calculate the K − -angle distribution function in the Gottfried-Jackson frame, using the polarization-transfer coefficients in the z direction. We find that it owns a complicated angle and energy dependences in the forward K + scattering region.

Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the fist several moments for the twist-3 distribution amplitudes (φ π p,σ and φ K p,σ) of the pion and kaon by applying the QCD sum rules. Our results show that, (i) the first three moments of φ K p and the first two moments of φ π p and φ π,K σ of the pion and kaon can be obtained with 30% uncertainty; (ii) the fourth moment of the φ π p and the second moment of the φ K σ can be obtained when the uncertainty are relaxed to 35%; (iii) the fourth moment of the φ π σ can be obtained only when the uncertainty are relaxed to 40%; (iv) we have m p 0π = 1.10 ± 0.08 GeV and m p 0K = 1.25 ± 0.15 GeV after including the α s-corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.