Kaon-Nucleon scattering states and potentials in the Skyrme model

We study the (anti)kaon nucleon interaction in the Skyrme model. The kaon field is introduced as a fluctuation around the rotating Skyrmion for the nucleon. As an extension of our previous work, we study scattering states and examine phase shifts in various kaon-nucleon channels. Then we study the interaction, where we find that it consists of central and spin-orbit components for isospin channels, $I = 0, 1$, with energy dependence and nonlocality. The interaction is then fitted to a Shr\"odinger equivalent local potential for s- and p-waves.Comment: 25 pages, 33 figures, and 10 table

Roper resonance in a quark-diquark model

We discuss a new description for the Roper resonance, the first nucleon excited state of JP = 1/2+, in a model of strong diquark correlations. Treating the scalar-isoscalar and axial-vector--isovector diquarks as independent degrees of freedom, two states having nucleon quantum numbers are constructed. Due to the scalar and axial-vector nature of the diquarks, the two nucleon states have different internal structure of spin and isospin. This yields the mass splitting of order several hundreds MeV, and hence the two states are identified with the nucleon and Roper. We demonstrate this scenario in a simple two channel problem.Comment: 10 pages, Proceedings of Hadron-nuclear physics probed by photon (HNP06), Feb. 16-18, 2006, JAEA, Kizu, Kyot

Kaon-Nucleon systems and their interactions in the Skyrme model

We study kaon-nucleon systems in the Skyrme model in a method based on the bound state approach of Callan-Klebanov but with the kaon around the physical nucleon of the rotating hedgehog. This corresponds to the variation after projection, reversing the order of semiclassical quantization of $1/N_c$ expansion. The method, however, is considered to be suited to the study of weakly interacting kaon-nucleon systems including loosely $\bar{K}N$ bound states such as $\Lambda(1405)$. We have found a bound state with binding energy of order ten MeV, consistent with the observed state. We also discuss the $\bar{K}N$ interaction and find that it consists of an attraction in the middle range and a repulsion in the short range

Composite and elementary nature of a resonance in the sigma model

We analyze the mixing nature of the low-lying scalar resonance consisting of the pipi composite and the elementary particle within the sigma model. A method to disentangle the mixing is formulated in the scattering theory with the concept of the two-level problem. We investigate the composite and elementary components of the sigma meson by changing a mixing parameter. We also study the dependence of the results on model parameters such as the cut-off value and the mass of the elementary sigma meson.Comment: 13 pages, 11 figures, 2 table

Path-integral approach in a chiral quark-diquark model to the nucleon structure and interactions

We study the structure of the nuclear force by using a path-integral hadronization approach in a chiral quark-diquark model. After the construction of the chiral quark-diquark model, we hadronize it to obtain a meson-baryon Lagrangian. The effective meson-baryon Lagrangian incorporates chiral symmetry and the composite description of the mesons and baryons. Using the effective meson-baryon Lagrangian we investigate the structure of the nuclear force in the simple case of neglecting the axial-vector diquark. It is shown that the meson-baryon Lagrangian contains two kinds of the nuclear force; the meson-exchange interaction and a quark-diquark loop interaction. It is also shown that the quark-diquark loop interaction consists of the scalar and vector interactions. The properties of these interactions are discussed.Comment: 13 pages, 9 figures. To appear in the proceedings of Workshop on Quark Nuclear Physics; Nuclear and Hadronic Systems and Quark Degrees of Freedom, Pyoungchang, Kangwondo, Korea, 22-24 Feb 200

Phenomenological study for the Theta+ and two-meson coupling

We examine several assignments of spin and parity for the pentaquark Theta+ state (J^P=1/2^{+,-}, 3/2^{+,-}) in connection with phenomenology of known baryon resonances, using a general framework based on the flavor symmetry. Assuming that the Theta+ belongs to an antidecuplet representation which mixes with an octet, we calculate the mass spectra of the flavor partners of the Theta+ based on the SU(3) symmetry. The decay widths of the Theta+ and nucleon partners are analyzed for the consistency check of the mixing angle obtained from the masses. It is found that a suitable choice of the mixing angle successfully reproduces the observed masses of exotics, when their spin and parity are assigned to be J^P=3/2^-, together with other nonexotic resonances of J^P=3/2^-. The decay widths of Theta -> KN, N(1520) -> pi N, and N(1700) -> pi N are also reproduced simultaneously. We then evaluate two-meson couplings of Theta+, using experimental information of nucleon partners decaying into pi pi N channels, in which the two pions are in scalar- and vector-type correlations. We examine two assignments of spin and parity J^P=1/2^+ and 3/2^-, for which the experimental spectra of known resonances with exotic baryons are properly reproduced by an octet-antidecuplet representation mixing scheme. Using the obtained coupling constants, total cross sections of the reactions pi- p -> K- Theta+ and K+ p -> pi+ Theta+ are calculated. Substantial interference of two terms may occur in the reaction processes for the J^P=1/2^+ case, whereas the interference effect is rather small for the 3/2^- case.Comment: 30 pages, 9 figures 9 tables, Talk given at International Workshop HNP06 at JAEA, Kizu, Japan, Feb. 16-18, 200

Structure of the Roper Resonance with Diquark Correlations

We study electromagnetic properties of the nucleon and Roper resonance in a chiral quark-diquark model including two kinds of diquarks needed to describe the nucleon: scalar and axial-vector diquarks. The nucleon and Roper resonance are described as superpositions of two quark-diquark bound states of a quark and a scalar diquark and of a quark and an axial-vector diquark. Electromagnetic form factors of the nucleon and Roper resonance are obtained from one-loop diagrams where the quark and diquarks are coupled by a photon. We include the effects of intrinsic properties of the diquarks: the intrinsic form factors both of the diquarks and the anomalous magnetic moment of the axial-vector diquark. The electric form factors of the proton and neutron reasonably agree with the experiments due to the inclusions of the diquark sizes, while the magnetic moments become smaller than the experimental values because of the scalar dominance in the nucleon. The charge radii of the Roper resonance are almost comparable with those of the nucleon.Comment: 19 pages, 15 figures. To appear in the proceedings of Workshop on Hadronic and Nuclear Physics 2007, Pusan National University, Korea, 22-24 Feb 200

Phenomenological study of two-meson couplings of Theta+

We evaluate two-meson couplings of Theta+, using experimental information of nucleon resonances decaying into pi pi N channels, in which the two pions are in scalar- and vector-type correlations. We examine two assignments of spin and parity of J^P=1/2^+ and 3/2^-, for which the experimental spectra of known resonances with exotic baryons are properly reproduced by an octet-antidecuplet representation mixing scheme. With the obtained coupling constants, total cross sections of the reactions pi- p -> K- Theta+ and K+ p -> pi+ Theta+ are calculated. Substantial interference of two terms may occur in the reaction processes for the J^P=1/2^+ case, whereas the interference effect is rather small for the 3/2^- case.Comment: RevTeX4, 13 pages, 17 figures, 2 tables, Version to appear in Phys. Rev.

Search of QCD phase transition points in the canonical approach of the NJL model

We study the Lee-Yang zeros in the canonical approach to search phase transition points at finite temperature and density in the Nambu-Jona-Lasinio (NJL) model as an effective model of QCD. The canonical approach is a promising method to avoid the sign problem in lattice QCD at finite density. We find that a set of Lee-Yang zeros computed with finite degrees of freedom can be extrapolated to those with infinite degrees of freedom, providing the correct phase transition point. We propose the present method as a useful method for actual lattice simulations for QCD.Comment: 7 pages, 7 figures and 1 tabl

Elementarity of composite systems

The "compositeness" or "elementarity" is investigated for s-wave composite states dynamically generated by energy-dependent and independent interactions. The bare mass of the corresponding fictitious elementary particle in an equivalent Yukawa model is shown to be infinite, indicating that the wave function renormalization constant Z is equal to zero. The idea can be equally applied to both resonant and bound states. In a special case of zero-energy bound states, the condition Z = 0 does not necessarily mean that the elementary particle has the infinite bare mass. We also emphasize arbitrariness in the "elementarity" leading to multiple interpretations of a physical state, which can be either a pure composite state with Z = 0 or an elementary particle with Z \ne 0. The arbitrariness is unavoidable because the renormalization constant Z is not a physical observable.Comment: 13 pages, 8 figures, title changed, publishe