arXiv subjects

Kiyomi Ikeda

Publications and source records attributed to Kiyomi Ikeda.

At least 37 records · Page 2Linked to original sources

arXiv2010

Triaxial superdeformation in $^{40}$Ar

Superdeformed (SD) states in $^{40}$Ar have been studied using the deformed-basis antisymmetrized molecular dynamics. Low energy states were calculated by the parity and angular momentum projection (AMP) and the generator coordinate method (GCM). Basis wave functions were obtained by the energy variation with a constraint on the quadrupole deformation parameter $β$, while other quantities such as triaxiality $γ$ were optimized by the energy variation. By the GCM calculation, an SD band was obtained just above the ground state (GS) band. The SD band involves a $K^π= 2^+$ side band due to the triaxiality. The calculated electric quadrupole transition strengths of the SD band reproduce the experimental values appropriately. Triaxiality is significant for understanding low-lying states.

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arXiv2009

Coulomb Breakup Reactions in Complex-Scaled Solutions of the Lippmann-Schwinger Equation

We propose a new method to describe three-body breakups of nuclei, in which the Lippmann-Schwinger equation is solved combining with the complex scaling method. The complex-scaled solutions of the Lippmann-Schwinger equation (CSLS) enables us to treat boundary conditions of many-body open channels correctly and to describe a many-body breakup amplitude from the ground state. The Coulomb breakup cross section from the 6He ground state into 4He+n+n three-body decaying states as a function of the total excitation energy is calculated by using CSLS, and the result well reproduces the experimental data. Furthermore, the two-dimensional energy distribution of the E1 transition strength is obtained and an importance of the 5He(3/2-) resonance is confirmed. It is shown that CSLS is a promising method to investigate correlations of subsystems in three-body breakup reactions of the weakly-bound nuclei.

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arXiv2009

Tensor-optimized shell model with bare nucleon-nucleon interaction for 4He

The pion exchange between nucleons generates a strong tensor interaction, which provides a large attractive contribution for the binding energy of nucleus. This non central tensor interaction is difficult to handle in the shell model framework, which hinders full understanding of nuclear structure. We develop the tensor-optimized shell model (TOSM) for the strong tensor interaction and now we are able to use bare nucleon-nucleon interaction with the help of the unitary correlation operator method (UCOM) for the short-range hard core. We adopt the nucleon-nucleon interaction, AV8', and calculate explicitly the ground state of $^4$He and make a detailed comparison with rigorous few-body model calculations. We show a large amount of success of the tensor-optimized shell model with bare nucleon-nucleon interaction for 4He.

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arXiv2008

Monopole Excitation to Cluster States

We discuss strength of monopole excitation of the ground state to cluster states in light nuclei. We clarify that the monopole excitation to cluster states is in general strong as to be comparable with the single particle strength and shares an appreciable portion of the sum rule value in spite of large difference of the structure between the cluster state and the shell-model-like ground state. We argue that the essential reasons of the large strength are twofold. One is the fact that the clustering degree of freedom is possessed even by simple shell model wave functions. The detailed feature of this fact is described by the so-called Bayman-Bohr theorem which tells us that SU(3) shell model wave function is equivalent to cluster model wave function. The other is the ground state correlation induced by the activation of the cluster degrees of freedom described by the Bayman-Bohr theorem. We demonstrate, by deriving analytical expressions of monopole matrix elements, that the order of magnitude of the monopole strength is governed by the first reason, while the second reason plays a sufficient role in reproducing the data up to the factor of magnitude of the monopole strength. Our explanation is made by analysing three examples which are the monopole excitations to the $0^+_2$ and $0^+_3$ states in $^{16}$O and the one to the $0^+_2$ state in $^{12}$C. The present results imply that the measurement of strong monopole transitions or excitations is in general very useful for the study of cluster states.

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arXiv2008

Systematic study of $^{9,10,11}$Li with the tensor and pairing correlations

We make a systematic study of Li isotopes (A=9,10,11) in the tensor optimized shell model for 9Li and treat the additional valence neutrons in the cluster model approach by taking into account the Pauli-blocking effect caused by the tensor and pairing correlations. We describe the tensor correlations in 9Li fully in the tensor-optimized shell model, where the variation of the size parameters of the single particle orbits is essential for getting strong tensor correlations. We have shown in our previous study that in $^{10,11}$Li the tensor and pairing correlations in 9Li are Pauli-blocked by additional valence neutrons, which make the p-shell configurations pushed up in energy. As a result, the $s^2$ valence neutron component increases to reveal the halo structure of 11Li and the inversion phenomenon of the single particle spectrum in 10Li arises. Following the previous study, we demonstrate the reliability of our framework by performing a detailed systematic analysis of the structures of $^{9,10,11}$Li, such as the charge radius, the spatial correlation of halo neutrons of 11Li and the electromagnetic properties of Li isotopes. The detailed effects of the Pauli-blocking on the spectroscopic properties of $^{10,11}$Li are also discussed. It is found that the blocking acts strongly for the 11Li ground state rather than for 10Li and for the dipole excited states of 11Li, which is mainly caused by the interplay between the tensor correlation in 9Li and the halo neutrons. The results obtained in these analyses clearly show that the inert core assumption of 9Li is not realistic to explain the anomalous structures observed in $^{10,11}$Li. For the dipole excitation spectrum of 11Li, the effect of the final state interactions is discussed in terms of the dipole strength function.

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arXiv2007

Resonances of 7He in the complex scaling method

We study the resonance spectroscopy of 7He in the 4He+n+n+n cluster model, where the motion of valence neutrons is described in the cluster orbital shell model. Many-body resonances are treated on the correct boundary condition as the Gamow states in the complex scaling method. We obtain five resonances and investigate their properties from the configurations. In particular, the 1/2- state is found in a low excitation energy of 1.1 MeV with a width of 2.2 MeV, while the experimental determination of the position of this state is not so clear. We also evaluate the spectroscopic factors of the 6He-n components in the obtained 7He resonances. The importance of the 6He(2+) state is shown in several states of 7He.

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arXiv2007

Roles of the tensor and pairing correlations on the halo formation in 11Li

We study the roles of the tensor and pairing correlations on the halo formation in 11Li with an extended 9Li+n+n model. We first solve the ground state of 9Li in the shell model basis by taking 2p-2h states using the Gaussian functions with variational size parameters to take into account the tensor correlation fully. In 11Li, the tensor and pairing correlations in 9Li are Pauli-blocked by additional two neutrons, which work coherently to make the configurations containing the 0p1/2 state pushed up and close to those containing the 1s1/2 state. Hence, the pairing interaction works efficiently to mix the two configurations by equal amount and develop the halo structure in 11Li. For 10Li, the inversion phenomenon of s- and p-states is reproduced in the same framework. Our model furthermore explains the recently observed Coulomb breakup strength and charge radius for 11Li.

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arXiv2007

Effect of the tensor force in the exchange channel on the spin-orbit splitting in 23F in the Hartree-Fock framework

We study the spin-orbit splitting ($ls$-splitting) for the proton d-orbits in 23F in the Hartree-Fock framework with the tensor force in the exchange channel. 23F has one more proton around the neutron-rich nucleus 22O. A recent experiment indicates that the ls-splitting for the proton d-orbits in 23F is reduced from that in 17F. Our calculation shows that the ls-splitting in 23F becomes smaller by about a few MeV due to the tensor force. This effect comes from the interaction between the valence proton and the occupied neutrons in the 0d5/2 orbit through the tensor force and makes the ls-splitting in 23F close to the experimental data.

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arXiv2007

Tensor correlation in 4He with the tensor-optimized shell model

We study the characteristics of the tensor correlation in $^4$He using a shell model type method. We treat the tensor force explicitly by performing a configuration-mixing calculation in the $2p2h$ basis and include single-particle states up to intermediately high angular momenta. We adopt the Gaussian expansion method for the quantitative description of the spatial shrinkage of the single-particle states to optimize the tensor correlation. We are able to describe the full strength of the tensor correlation for $^4$He in the shell model type method by realizing convergence. We call this model the tensor-optimized shell model. It is found that in $^4$He, three specific $2p2h$ configurations are strongly coupled with the $(0s)^4$ configuration due to the characteristic features of the tensor operator.

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arXiv2006

Study of the effect of the tensor correlation in oxygen isotopes with the charge- and parity-projected Hartree-Fock method

Recently, we developed a mean-field-type framework which treats the correlation induced by the tensor force. To exploit the tensor correlation we introduce single-particle states with the parity and charge mixing. To make a total wave function have a definite charge number and a good parity, the charge number and parity projections are performed. Taking a variation of the projected wave function with respect to single-particle states a Hartree-Fock-like equation, the charge- and parity-projected Hartree-Fock equation, is obtained. In the charge- and parity-projected Hartree-Fock method, we solve the equation selfconsistently. In this paper we extend the charge- and parity-projected Hartree-Fock method to include a three-body force, which is important to reproduce the saturation property of nuclei in mean-field frameworks. We apply the charge- and parity-projected Hartree-Fock method to sub-closed-shell oxygen isotopes (14O, 16O, 22O, 24O, and 28O) to study the effect of the tenor correlation and its dependence on neutron numbers. We obtain reasonable binding energies and matter radii for these nuclei. It is found that relatively large energy gains come from the tensor force in these isotopes and there is the blocking effect by occupied neutron orbits on the tensor correlation.

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arXiv2006

Study of the effect of the tensor correlation on the alpha clustering in 8Be with the charge- and parity-projected Hartree-Fock method

We study the effect of the tensor correlation in the alpha clustering in 8Be. We take as the wave function of the alpha particle the one calculated by the charge- and parity-projected Hartree- Fock method, which was proposed by us recently. We use the wave function in a cluster-model calculation. The expectation value of the potential energy from the tensor force is almost double of that in the alpha particle. The energy surface as the function of the relative distance of two alpha particles becomes much steeper in an inner region by the inclusion of the tensor correlation in the wave function of the alpha particle. This is caused by the p-state mixing induced by the tensor correlation. By superposing the wave function with different relative distances, the reasonable binding energy of 8Be is obtained.

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arXiv2005

Explicit treatment of tensor force with a method of Antisymmetrized Molecular Dynamics

In order to treat tensor force explicitly, we propose a microscopic model for nuclear structure based on antisymmetrized molecular dynamics (AMD). As a result of the present study, it is found that some extentions of the AMD method are effective to incorporate the tensor correlation into wave functions. Calculating the deuteron, triton and $^4$He with the extended version of AMD, we obtained solutions that have large contribution of the tensor force. By analyzing the wave funtion of $^4$He, it is found that its single-particle orbits are composed of normal-size $0s$ orbits and shrunk $p$ orbits so as to gain the tensor force.

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arXiv2005

Tensor correlation in 4He and its Effect on the doublet splitting in 5He

We investigate the role of tensor correlation on the structures of \nuc{4}{He} and its effect on the doublet splitting in \nuc{5}{He}. We perform a configuration mixing calculation in the shell model type bases to represent the tensor correlation for $^4$He. It is found that our model describes the characteristics of the tensor correlation, which is represented by an admixture of the $0s_{1/2}$ configuration with a spatially modified $0p_{1/2}$ orbit. For $^5$He, we solve a coupled OCM equation for an extended $^4$He+$n$ model, while taking into account the tensor correlation in the $^4$He cluster. It is shown that the tensor correlation produces the Pauli blocking, in particular, for the $J^π={1/2}^-$ state, and its effect causes about half of the p-wave doublet splitting in $^5$He. This indicates that the strength of the effective spin-orbit interaction should be reduced by about half from the conventional one. We obtain a reliable $^4$He-$n$ interaction, including the tensor correlation, which further improves the behavior of the $d$- and $f$-wave phase shifts in the $^4$He+$n$ system.

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arXiv2004

Charge- and parity-projected Hartree-Fock method for the strong tensor correlation and its application to the alpha particle

We propose a new mean-field-type framework which can treat the strong correlation induced by the tensor force. To treat the tensor correlation we break the charge and parity symmetries of a single-particle state and restore these symmetries of the total system by the projection method. We perform the charge and parity projections before variation and obtain a Hartree-Fock-like equation, which is solved self-consistently. We apply the Hartree-Fock-like equation to the alpha particle and find that by breaking the parity and charge symmetries, the correlation induced by the tensor force is obtained in the projected mean-field framework. We emphasize that the projection before the variation is important to pick up the tensor correlation in the present framework.

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arXiv2004

New mean field theory with the parity and charge mixing for the pion in nuclei

We give a brief review on the important role of the pion-exchange interaction characterized by the strong tensor force. In order to illustrate the role of the pion, we have proposed a new mean field theory with the charge and parity mixing, by which the pion is treated explicitly in the mean field framework. We introduce the essence of the new mean field theory and illustrate the calculated results of the pion (tensor force) correlation by taking the alpha particle as an example.

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arXiv2004

Chiral Symmetry and Finite Pion Mean Field in Nuclei

We introduce the chiral symmetry in the description of finite nuclei with the hope to unify the hadron and nuclear physics. This trial becomes possible by introducing finite pion mean field, which contributes largely to enhance the spin-orbit splitting so as to provide the j-j magic number. We discuss the qualitative consequence of the finite pion mean field for various observables.

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arXiv2004

Charge- and parity-projected Hartree-Fock study with the tensor force of light nuclei

We propose a mean field framework in which the charge and the parity symmetries of a single-particle state are broken. We break these symmetries to incorporate the correlation induced by the tensor force into a nuclear mean field model. We perform the charge- and the parity projections before variation and obtain a Hartree-Fock-like equation (charge- and parity-projected Hartree-Fock equation), which is solved self-consistently. We apply the Hartree-Fock-like equation to the alpha particle and find that, by breaking the parity and the charge symmetries, the correlation induced by the tensor force is obtained.

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arXiv2002

Extended 9Li+n+n three-body model of 11Li with the pairing correlation in 9Li

We discuss the binding mechanism of 11Li based on an extended three-body model of Li+n+n. In the model, we take into account the pairing correlation of p-shell neutrons in 9Li, in addition to that of valence neutrons outside the 9Li nucleus, and solve the coupled-channel two- and three-body problems of 10Li and 11Li, respectively. The results show that degrees of freedom of the pairing correlation in 9Li play an important role in the structure of 10Li and 11Li. In 10Li, the pairing correlation in 9Li produces a so-called pairing-blocking effect due to the presence of valence neutron, which degenerates s- and p-wave neutron orbits energetically. In 11Li, on the other hand, the pairing-blocking effect is surpassed by the core-n interaction due to two degrees of freedom of two valence neutrons surrounding 9Li, and as a result, the ground state is dominated by the p-shell closed configuration and does not show a spatial extension with a large r.m.s. radius. These results indicate that the pairing correlation is realized differently in odd- and even-neutron systems of 10Li and 11Li. We further improve the tail part of the 9Li-n interaction, which works well to reproduce the observed large r.m.s. radius in 11Li.

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