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A. Hosaka

Publications and source records attributed to A. Hosaka.

At least 91 records · Page 5Linked to original sources
arXiv2004

Threshold production of the $Θ^+$ in a polarized proton reaction

We compute cross sections of $Θ^+$ production near threshold for a polarized proton reaction, $\vec p \vec p \to Σ^+ Θ^+$ which was recently proposed to determine unambiguously the parity of $Θ^+$. Within theoretical uncertainties 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.

hep-ph↗
arXiv2003

Chiral Sigma Model with Pion Mean Field in Finite Nuclei

The properties of infinite matter and finite nuclei are studied by using the chiral sigma model in the framework of the relativistic mean field theory. We reconstruct an extended chiral sigma model in which the omega meson mass is generated dynamically by the sigma condensation in the vacuum in the same way as the nucleon mass. All the parameters of chiral sigma model are essentially fixed from the hadron properties in the free space. In nuclear matter, the saturation property comes out right, but the incompressibility is too large and the scalar and vector potentials are about a half of the phenomenological ones, respectively. This fact is reflected to the properties of finite nuclei. We calculate N = Z even-even mass nuclei between N = 16 and N = 34. The extended chiral sigma model without the pion mean field leads to the result that the magic number appears at N = 18 instead of N = 20 and the magic number does not appear at N = 28 due to the above mentioned nuclear matter properties. The latter problem, however, could be removed by the introduction of the finite pion mean field with the appearance of the magic number at N = 28. We find that the energy differences between the spin-orbit partners are reproduced by the finite pion mean field which is completely a different mechanism from the standard spin-orbit interaction.

nucl-th↗
arXiv2003

Structure of the nuclear force in a chiral quark-diquark model

We discuss the structure of the nuclear force using a lagrangian derived from hadronization of a chiral quark and diquark model. A generalized trace log formula including meson and nucleon fields is expanded to the order in which relevant terms emerge. It is shown that the nuclear force is composed of long and medium range parts of chiral meson exchanges and short range parts of quark-diquark exchanges. The ranges of the scalar and vector interactions coincide well with those of sigma ($σ$) and omega ($ω$) meson exchanges if the size of the nucleon core of a quark-diquark bound state is adjusted appropriately.

hep-ph↗
arXiv2003

A Method to Unambiguously Determine the Parity of the Theta+ Pentaquark

With the recent discovery of the $Θ(1540)$ pentaquark, the question of its parity is paramount since this will constrain the correct description of its internal structure. We show that the measurement of the spin singlet and triplet cross sections for the reaction $\vec{p}\vec{p} \to Σ^+ Θ^+$ will unambiguously determine the parity of the $Θ^+$.

hep-ph↗
arXiv2003

Determining the $Θ^+$ quantum numbers through the $K^+p\to π^+K^+n$ reaction

We study the $K^+p\to π^+K^+n$ reaction with some kinematics suited to the production of the $Θ^+$ resonance recently observed. We show that, independently of the quantum numbers of the $Θ^+$, a resonance signal is always observed in the $K^+$ forward direction. In addition, we also show how a combined consideration of the strength at the peak, and the angular dependence of polarization observables can help determine the $Θ^+$ quantum numbers using the present reaction.

nucl-th↗
arXiv2003

$Λ(1405)$ production in the $π^-p\to K^0πΣ$ reaction

We discuss the mechanisms that lead to $Λ(1405)$ production in the $π^-p\to K^0πΣ$ reaction. The problem has gained renewed interest after different works converge to the conclusion that there are two resonances around the region of 1400 MeV, rather than one, and that they couple differently to the $πΣ$ and $\bar{K}N$ channels. We look at the dynamics of that reaction and find two mechanisms which eventually filter each one of the resonances, leading to very different shapes of the $πΣ$ invariant mass distributions. The combination of the two mechanisms leads to a shape of this distribution compatible with the experimental measurements.

nucl-th↗
arXiv2003

Photoproduction of Theta baryon from the neutron

We study photoproduction reactions for Theta^+, which was recently observed as a candidate of an exotic five quark state uudd(bar s). We employ effective lagrangian interactions in the linear and non-linear formalism of chiral symmetry and investigate two cases of spin and parity of Theta^+, J^P = 1/2^+ and 1/2^-. We calculate cross sections and discuss possibilities to discriminate one from the other.

hep-ph↗
arXiv2003

Regulariztion dependence of S=0 and S=-1 meson-baryon system in the chiral unitary model

We investigate the dependence of s-wave meson-baryon scattering amplitudes on different regularizations within the framework of the chiral unitary model. We employ two different regularization schemes, i.e. dimensional and form-factor regulariaztions to tame the divergences in the model. We also study the analytic structures of T-matrices, using those regularization schemes. We find that while the form-factor regularizaion produces almost the same results as the dimensional regularization did, the on-shell approximation is to some extent limited in the case of the form-factor regularization. Having chosen parameters properly, we show that the regularization dependences can be minimized.

hep-ph↗
arXiv2003

Chiral symmetry aspects of positive and negative parity baryons

Chiral 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 the reactions of pion and eta productions.

hep-ph↗
arXiv2003

Magnetic moments of the N(1535) resonance in the chiral unitary model

We calculate the magnetic moments of the N(1535) resonance using the chiral unitary model, where the resonance is dynamically generated in the scatterings of the lowest-lying mesons and baryons. We obtain the magnetic moments of the resonance as +1.1 and -0.25 for p(1535) and n(1535), respectively, in units of the nuclear magneton. We discuss the origin of these numbers within the chiral unitary model, then we compare the present results with those of the quark model and the chiral doublet model. The possibility to observe the magnetic moments in experiments is also investigated.

nucl-th↗
arXiv2003

Flavor SU(3) breaking effects in the chiral unitary model for meson-baryon scatterings

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.

nucl-th↗
arXiv2003

Chiral phase properties of finite size quark droplets in the Nambu--Jona-Lasinio model

Chiral phase properties of finite size hadronic systems are investigated within the Nambu--Jona-Lasinio model. Finite size effects are taken into account by making use of the multiple reflection expansion. We find that, for droplets with relatively small baryon numbers, chiral symmetry restoration is enhanced by the finite size effects. However the radius of the stable droplet does not change much, as compared to that without the multiple reflection expansion.

hep-ph↗
arXiv2002

Separable Kernel of Nucleon-Nucleon Interaction in the Bethe-Salpeter Approach for J=0,1

The solution for the nucleon-nucleon T matrix in the framework of the covariant Bethe-Salpeter approach for a two spin-one-half particle system with a separable kernel of interaction is analyzed. The explicit analytical connection between parameters of the separable kernel and low energy scattering parameters, deuteron binding energy and phase shifts is established.Covariant separable kernels for positive-energy partial channels with total angular momentum J=0 (1S0+, 3P0+) and J=1 (3S1+-3D1+, 1P1+, 3P1+) are constructed by using obtained relations.

nucl-th↗
arXiv2002

Path-integral hadronization for the nucleon and its interactions

Nucleon structure and the origin and nature of the nuclear force are investigated in the context of a QCD-based effective field theory and the path-integral method of hadronization. We start from a microscopic model of quarks and diquarks where the gluons have been integrated out. In particular, we use the chiral Nambu-Jona-Lasinio model to describe quark dynamics and assume that the nucleon can be conceived as a quark-diquark relativistic bound state. The hadronization method is then used to rewrite the problem in terms of the physical meson and nucleon degrees of freedom. Next, by employing a loop and derivative expansion of the resulting quark/diquark determinants, we arrive at an effective chiral meson-nucleon Lagrangian. Nucleon properties such as mass, coupling constants, electromagnetic radii, anomalous magnetic moments, and form factors are derived using a theory of at most two free parameters.

nucl-th↗
arXiv2002

Mass Dependence of M3Y-Type Interactions and the Effects of Tensor Correlations

The mass dependence of the M3Y-type effective interactions and the effects of tensor correlations are examined. Two-body nuclear matrix elements are obtained by the lowest order constrained variational (LOCV) technique with and without tensor correlations. We have found that the tensor correlations are important especially in the triplet-even (TE) and tensor-even (TNE) channels in order to reproduce the G-matrix elements obtained previously. Then M3Y-type potentials for inelastic scattering are obtained by fitting our two-body matrix elements to those of a sum of Yukawa functions for the mass numbers A=24, A=40 and A=90.

nucl-th↗
arXiv2002

Magnetic moments of the Lambda(1405) and Lambda(1670) resonances

By using techniques of unitarized chiral perturbation theory, where the $Λ(1405)$ and $Λ(1670)$ resonances are dynamically generated, we evaluate the magnetic moments of these resonances and their transition magnetic moment. The results obtained here differ appreciably from those obtained with existing quark models. The width for the $Λ(1670) \to Λ(1405) γ$ transition is also evaluated leading to a branching ratio of the order of $2 \times 10^{-6}$.

hep-ph↗
arXiv2002

Determination of the axial coupling constant $g_{A}$ in the linear representations of chiral symmetry

If a baryon field belongs to a certain linear representation of chiral symmetry of $SU(2) \otimes SU(2)$, the axial coupling constant $g_{A}$ can be determined algebraically from the commutation relations derived from the superconvergence property of pion-nucleon scattering amplitudes. This establishes an algebraic explanation for the values of $g_{A}$ of such as the non-relativistic quark model, large-$N_{c}$ limit and the mirror assignment for two chiral partner nucleons. For the mirror assignment, the axial charges of the positive and negative parity nucleons have opposite signs. Experiments of eta and pion productions are proposed in which the sign difference of the axial charges can be observed.

hep-ph↗