288 research outputs found

### 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

- â€¦