Hyperons analogous to the \Lambda(1405)

The low mass of the $\Lambda(1405)$ hyperon with $j^P = 1/2^-$, which is higher than the ground state $\Lambda(1116)$ mass by 290 MeV, is difficult to understand in quark models. We analyze the hyperon spectrum in the bound state approach of the Skyrme model that successfully describes both the $\Lambda(1116)$ and the $\Lambda(1405)$. This model predicts that several hyperon resonances of the same spin but with opposite parity form parity doublets that have a mass difference of around 300 MeV, which is indeed realized in the observed hyperon spectrum. Furthermore, the existence of the $\Xi(1620)$ and the $\Xi(1690)$ of $j^P=1/2^-$ is predicted by this model. Comments on the $\Omega$ baryons and heavy quark baryons are made as well.Comment: 4 pages, talk presented at the Fifth Asia-Pacific Conference on Few-Body Problems in Physics 2011 (APFB2011), Aug. 22-26, 2011, Seoul, Kore

Short-range repulsion and isospin dependence in the KN system

The short-range properties of the KN interaction are studied within the meson-exchange model of the Juelich group. Specifically, dynamical explanations for the phenomenological short-range repulsion, required in this model for achieving agreement with the empirical KN data, are explored. Evidence is found that contributions from the exchange of a heavy scalar-isovector meson (a_0(980)) as well as from genuine quark-gluon exchange processes are needed. Taking both mechanisms into account a satisfactory description of the KN phase shifts can be obtained without resorting to phenomenological pieces.Comment: 26 pages, 5 figure

Excited Baryons in Lattice QCD

We present first results for the masses of positive and negative parity excited baryons calculated in lattice QCD using an O(a^2)-improved gluon action and a fat-link irrelevant clover (FLIC) fermion action in which only the irrelevant operators are constructed with APE-smeared links. The results are in agreement with earlier calculations of N^* resonances using improved actions and exhibit a clear mass splitting between the nucleon and its chiral partner. An correlation matrix analysis reveals two low-lying J^P=(1/2)^- states with a small mass splitting. The study of different Lambda interpolating fields suggests a similar splitting between the lowest two Lambda1/2^- octet states. However, the empirical mass suppression of the Lambda^*(1405) is not evident in these quenched QCD simulations, suggesting a potentially important role for the meson cloud of the Lambda^*(1405) and/or a need for more exotic interpolating fields.Comment: Correlation matrix analysis performed. Increased to 400 configurations. 22 pages, 13 figures, 15 table

Initial State Interactions for K−K^--Proton Radiative Capture

The effects of the initial state interactions on the $K^--p$ radiative capture branching ratios are examined and found to be quite sizable. A general coupled-channel formalism for both strong and electromagnetic channels using a particle basis is presented, and applied to all the low energy $K^--p$ data with the exception of the {\it 1s} atomic level shift. Satisfactory fits are obtained using vertex coupling constants for the electromagnetic channels that are close to their expected SU(3) values.Comment: 16 pages, uses revte

Kaon-Nucleon Scattering Amplitudes and Z∗^*-Enhancements from Quark Born Diagrams

We derive closed form kaon-nucleon scattering amplitudes using the ``quark Born diagram" formalism, which describes the scattering as a single interaction (here the OGE spin-spin term) followed by quark line rearrangement. The low energy I=0 and I=1 S-wave KN phase shifts are in reasonably good agreement with experiment given conventional quark model parameters. For $k_{lab}> 0.7$ Gev however the I=1 elastic phase shift is larger than predicted by Gaussian wavefunctions, and we suggest possible reasons for this discrepancy. Equivalent low energy KN potentials for S-wave scattering are also derived. Finally we consider OGE forces in the related channels K$\Delta$, K$^*$N and K$^*\Delta$, and determine which have attractive interactions and might therefore exhibit strong threshold enhancements or ``Z$^*$-molecule" meson-baryon bound states. We find that the minimum-spin, minimum-isospin channels and two additional K$^*\Delta$ channels are most conducive to the formation of bound states. Related interesting topics for future experimental and theoretical studies of KN interactions are also discussed.Comment: 34 pages, figures available from the authors, revte

Z^* Resonances: Phenomenology and Models

We explore the phenomenology of, and models for, the Z^* resonances, the lowest of which is now well established, and called the Theta. We provide an overview of three models which have been proposed to explain its existence and/or its small width, and point out other relevant predictions, and potential problems, for each. The relation to what is known about KN scattering, including possible resonance signals in other channels, is also discussed.Comment: 29 pages, uses RevTeX4; expanded version (published form

Role of \mth{\Delta} exchange for \mth{p \bar p} annihilation into two-pion and three-pion channels

\mth{p\bar{p}} annihilation into two pions and three pions is studied in a baryon exchange model. Annihilation diagrams involving nucleon as well as $\Delta$-resonance exchanges are included consistently in the two- and three-pion channels. Effects from the initial-state interaction are fully taken into account. A comparison of the influence of the $\Delta$ exchange on the considered annihilation channels is made and reveals that its importance for three-pion annihilation is strongly reduced as compared to two-pion annihilation. It is found that annihilation into three uncorrelated pions can yield up to 10% of the total experimentally observed three-pion annihilation cross-section

Pion-nucleon scattering in the cloudy bag model

We investigate s- and p-wave pion-nucleon scattering in the volume-coupling version of the cloudy bag model. The earlier conclusions about the nature of the Δ(1232), based on surface coupling, are not altered. This model also provides a good description of the ‘‘small’’ p-wave phase shifts, and the s-wave scattering lengths. However, there are indications from the s waves at energies above 100 MeV, and from the channel, that some physics is still missing.E. A. Veit, B. K. Jennings, and A. W. Thoma

Removal Of Nickel(ii) Ions From Aqueous Solution By Biosorption In A Fixed Bed Column: Experimental And Theoretical Breakthrough Curves

The nickel(II) ions biosorption process by marine algae Sargassum filipendula in a fixed bed column was investigated for the following experimental conditions: temperature = 30 °C and pH 3.0. The experimental breakthrough curves were obtained for the following chosen flow rates 0.002, 0.004, 0.006, and 0.008 L/min. A mathematical model was developed to describe the nickel ion sorption in a fixed bed column. The model of three partial differential equations (PDE) has considered the hydrodynamics throughout the fixed bed column as well as the sorption process in the liquid and solid phases. The internal and external mass transfer limitations were considered, as well. The nickel ion sorption kinetics has been studied utilizing the Langmuir isotherm. The PDE of the system were discretized in the form of ordinary differential equations (ODE) and were solved for the given initial and boundary conditions using the finite volume method. A new correlation for external mass transfer coefficient was developed. Some of the model parameters were experimentally determined (ε, dp) where the others such as (KF, KS) were evaluated on the base of experimental data parameters. The identification procedure was based on the least square statistical method. The robustness and flexibility of the developed model was checked out using four sets of experimental data and the predictive power of the model was evaluated to be good enough for the all studied cases. The developed model can be useful tool for nickel ion removal process optimization and design of fixed bed columns using biomass of S. filipendula as a sorbent. © 2006 Elsevier B.V. All rights reserved.302184191Akhtar, N., Iqbal, J., Iqbal, M., Removal and recovery of nickel (II) from aqueous solution by loofa sponge-immobilized biomass of Chlorela sorokiniana: characterization studies (2004) J. Hazard. 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