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In the past ** Atsushi Hosaka** has collaborated on articles with

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AbstractThe first negative parity state of the nucleon resonance N(1535) is predominantly described as an eta-nucleon (skyrmion) bound state, which subsequently couples to the pion-nucleon system. Solving the two channel problem approximately, it is shown how bound state properties are improved to describe the nature of the resonance.

AbstractWe calculate higher order contributions to spin-isospin quantities such as isovector axial vector coupling constant gA and the isovector magnetic moment μl=1 in the chiral bag model. Quark contributions to those quantities are fully evaluated including vacuum polarization effects up to the order of Ω1 in the cranking method for spin and isospin projection. It is confirmed that the higher order corrections have a sizable effect on gA at reasonable bag radii. The chiral bag model now has the correct limits of the MIT bag model at R → ∞ and the Skyrme model at R → 0.

AbstractWe reanalize the chiral bag model with the inclusion of higher order terms in the cranking method, which provides a systematic expansion in powers of the angular velocity Ω. Emphasis is placed on the large bag limit, where the previous calculations could not reproduce the MIT bag results for such quantities as the axial vector coupling constant gA. We show that the correct limit is recovered by including a term of order Ω. The empirical value for gA (=1.25) is then reproduced at the bag radius R≈0.6 fm.

AbstractWe review the chiral bag model for the nucleon at low energy. The model is a hybrid model of quark and meson degrees of freedom, interpolating the two limits of the Skyrme model at R → 0 and the MIT bag model at R → ∞, where R is the bag radius. Baryon number one (B = 1) solutions are obtained in the semiclassical method, where the nucleon is regarded as a slowly rotating hedgehog. We investigate static properties of the nucleon such as masses and magnetic moments as functions of R, first in the original chiral bag model and second in the models with vector mesons. We find a reasonably good description for the nucleon in both cases at an intermediate bag radius R ~ 0.6 fm. Results of the model calculations are then re-derived using a group theoretical method in the large-Nc limit.

AbstractWe compute the cross sections of the Θ+ production near threshold for a polarized proton reaction, p→p→→Σ+Θ+ which was recently proposed to determine unambiguously the parity of Θ+. Within theoretical uncertainties the cross sections for the allowed spin configuration are estimated; it is of order of one microbarn for the positive parity Θ+ and about 1/10 microbarn for the negative parity Θ+ in the threshold energy region, where the s-wave component dominates.

AbstractWe study electromagnetic transitions of excited baryons in a deformed oscillator quark model, where baryon excited states are described as rotational bands of deformed intrinsic states. We describe all necessary tools to compute transition amplitudes in multipole basis, which are then related to the commonly used helicity amplitudes. We pay a special attention on the sign of the amplitudes as well as their absolute values by computing the photon and pion couplings simultaneously. We have found that the effect of deformation on the transition amplitudes is rather weak. The difficulty in reproducing the empirical amplitude of the Roper state is discussed.

AbstractChiral symmetry aspects for baryon properties are studied. After a brief discussion on general framework, we introduce two distinctive chiral group representations for baryons: the naive and mirror assignments. Using linear sigma models, nucleon properties are studied in both representations. Finally, we propose an experiment to distinguish the two assignments in pion and eta productions.

AbstractWe discuss the possible existence of exotic dibaryons with a heavy antiquark, being realized as three-body systems, D¯(⁎)NN and B(⁎)NN. These are genuinely exotic states with no quark–antiquark annihilation. We consider the heavy quark spin and chiral symmetries, and introduce the one pion exchange potential between a D¯(⁎) (B(⁎)) meson and a nucleon N. As for the NN interaction, we employ the Argonne v8′ potential. By solving the coupled-channel equations for PNN and P⁎NN (P(⁎)=D¯(⁎) and B(⁎)), we find bound states for (I,JP)=(1/2,0−) as well as resonant states for (I,JP)=(1/2,1−) both in D¯(⁎)NN and B(⁎)NN systems. We also discuss the heavy quark limit, and find that the spin degeneracy is realized in the bound states with (I,JP)=(1/2,0−) and (1/2,1−).

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