arXiv subjects

Hiroshi Toki

Publications and source records attributed to Hiroshi Toki.

At least 55 records · Page 3Linked to original sources

arXiv2012

Relativistic Chiral Mean Field Model for Finite Nuclei

We present a relativistic chiral mean field (RCMF) model, which is a method for the proper treatment of pion-exchange interaction in the nuclear many-body problem. There the dominant term of the pionic correlation is expressed in two-particle two-hole (2p-2h) states with particle-holes having pionic quantum number, J^{pi}. The charge-and-parity-projected relativistic mean field (CPPRMF) model developed so far treats surface properties of pionic correlation in 2p-2h states with J^{pi} = 0^{-} (spherical ansatz). We extend the CPPRMF model by taking 2p-2h states with higher spin quantum numbers, J^{pi} = 1^{+}, 2^{-}, 3^{+}, ... to describe the full strength of the pionic correlation in the intermediate range (r > 0.5 fm). We apply the RCMF model to the ^{4}He nucleus as a pilot calculation for the study of medium and heavy nuclei. We study the behavior of energy convergence with the pionic quantum number, J^{pi}, and find convergence around J^{pi}_{max} = 6^{-}. We include further the effect of the short-range repulsion in terms of the unitary correlation operator method (UCOM) for the central part of the pion-exchange interaction. The energy contribution of about 50% of the net two-body interaction comes from the tensor part and 20% comes from the spin-spin central part of the pion-exchange interaction.

nucl-th↗

arXiv2012

Tensor-optimized shell model for the Li isotopes with a bare nucleon-nucleon interaction

We study the Li isotopes systematically in terms of the tensor-optimized shell model (TOSM) by using a bare nucleon-nucleon interaction as the AV8' interaction. The short-range correlation is treated in the unitary correlation operator method (UCOM). Using the TOSM+UCOM approach, we investigate the role of the tensor force on each spectrum of the Li isotopes. It is found that the tensor force produces quite a characteristic effect on various states in each spectrum and those spectra are affected considerably by the tensor force. The energy difference between the spin-orbit partner, the p1/2 and p3/2 orbits of the last neutron, in 5Li is caused by opposite roles of the tensor correlation. In 6Li, the spin-triplet state in the LS coupling configuration is favored energetically by the tensor force in comparison with jj coupling shell model states. In 7,8,9Li, the low-lying states containing extra neutrons in the p3/2 orbit are favored energetically due to the large tensor contribution to allow the excitation from the 0s orbit to the p1/2 orbit by the tensor force. Those three nuclei show the jj coupling character in their ground states which is different from 6Li.

nucl-th↗

arXiv2011

Role of the tensor interaction in He isotopes with a tensor-optimized shell model

We studied the role of the tensor interaction in He isotopes systematically on the basis of the tensor-optimized shell model (TOSM). We use a bare nucleon-nucleon interaction AV8 obtained from nucleon-nucleon scattering data. The short-range correlation is treated in the unitary correlation operator method (UCOM). Using the TOSM+UCOM approach, we investigate the role of tensor interaction on each spectrum in He isotopes. It is found that the tensor interaction enhances the LS splitting energy observed in 5He, in which the p1/2 and p3/2 orbits play different roles on the tensor correlation. In {6,7,8}He, the low-lying states containing extra neutrons in the p3/2 orbit gain the tensor contribution. On the other hand, the excited states containing extra neutrons in the p1/2 orbit lose the tensor contribution due to the Pauli-blocking effect with the 2p2h states in the 4He core configuration.

nucl-th↗

arXiv2011

Tensor-optimized few-body model for s-shell nuclei

As a new scheme of treating the tensor interaction of the nucleon-nucleon interaction, there is a proposal of a tensor-optimized shell-model (TOSM) for the study of medium and heavy nuclei. The TOSM includes the deuteron-like tensor correlation and provides quite a good reproduction of the binding energy and the size of $^4$He as compared with rigorous few body calculations. We propose a tensor-optimized few-body model (TOFM) using the spirit of the TOSM approximation in the few body framework with bare nucleon-nucleon interaction. We find that the TOFM can account for the strength of the tensor interaction very well and almost reproduces the full energy and various energy components as compared with rigorous few body calculations.

nucl-th↗

arXiv2010

Di-neutron clustering and deuteron-like tensor correlation in nuclear structure focusing on 11Li

11Li is a Borromean nucleus, where two out of three objects as 9Li + n and two neutrons independently do not form bound systems. Two neutrons should form a di-neutron cluster in the nuclear field generated by the 9Li core nucleus. We treat di-neutron clustering by solving the two neutron relative wave function precisely by using the bare nucleon-nucleon interaction so that the spatial clustering structure is obtained quantitatively within the whole 11Li nucleus. This di-neutron clustering is an essential dynamics to form the halo structure by making a compact di-neutron cluster, which distributes loosely around the 9Li core. The di-neutron clustering is a new concept and is a general phenomenon in neutron skin and neutron halo nuclei. This quantitative description of di-neutron clustering has made it necessary to consider another important deuteron-like tensor correlation, which is caused by strong tensor interaction in the nucleon-nucleon interaction. The tensor interaction originates from pion exchange and known to provide large attraction to form the 4He nucleus. The unique feature of the tensor correlation is to make highly correlated deuteron-like excitation, which interferes with shell model like structure in a unique way. This dynamical effect removes the magic number effect and makes easy the participation of the s-wave neutrons. Hence, there are pairing and deuteron-like tensor correlations in addition to the mean field structure in 9Li. The combined system of two additional neutrons with the correlated 9Li provides the halo phenomenon, in which the di-neutron clustering develops with the help of large s-wave component caused by the deuteron-like tensor correlation. In this lecture note, we would like to introduce these two new concepts in a systematic manner and fill a gap between the halo phenomenon and the microscopic reason for this interesting phenomenon.

nucl-th↗

arXiv2010

Light Scalar Meson sigma(600) in QCD Sum Rule with Continuum

The light scalar meson sigma(600) is known to appear at low excitation energy with very large width on top of continuum states. We investigate it in the QCD sum rule as an example of resonance structures appearing above the corresponding thresholds. We use all the possible local tetraquark currents by taking linear combinations of five independent local ones. We ought to consider the pi-pi continuum contribution in the phenomenological side of the QCD sum rule in order to obtain a good sum rule signal. We study the stability of the extracted mass against the Borel mass and the threshold value and find the sigma(600) mass at 530 MeV +- 40 MeV. In addition we find the extracted mass has an increasing tendency with the Borel mass, which is interpreted as caused by the width of the resonance.

hep-ph↗

arXiv2010

Pseudoscalar Mesons in the SU(3) Linear Sigma Model with Gaussian Functional Approximation

We study the SU(3) linear sigma model for the pseudoscalar mesons in the Gaussian Functional Approximation (GFA). We use the SU(3) linear sigma model Lagrangian with nonet scalar and pseudo-scalar mesons including symmetry breaking terms. In the GFA, we take the Gaussian Ansatz for the ground state wave function and apply the variational method to minimize the ground state energy. We derive the gap equations for the dressed meson masses, which are actually just variational parameters in the GFA method. We use the Bethe-Salpeter equation for meson-meson scattering which provides the masses of the physical nonet mesons. We construct the projection operators for the flavor SU(3) in order to work out the scattering T-matrix in an efficient way. In this paper, we discuss the properties of the Nambu-Goldstone bosons in various limits of the chiral $U_L(3)\times U_R(3)$ symmetry.

hep-ph↗

arXiv2009

Coulomb gauge gluon propagator on anisotropic lattices

We calculate the transverse and the time-time components of the Coulomb-gauge gluon propagator in SU(3) lattice Yang-Mills theory both on isotropic and anisotropic lattices. The problem of scaling violation observed on the isotropic lattice is drastically reduced as the anisotropy increases; namely, the system approaches the Hamiltonian limit. In the infrared region, the transverse gluon propagator exhibits a turnover and the temporal gluon propagator shows divergent behavior.

hep-lat↗

arXiv2009

Relativistic description of BCS-BEC crossover in nuclear matter

We study theoretically the di-neutron spatial correlations and the crossover from superfluidity of neutron Cooper pairs in the $^1S_0$ pairing channel to Bose-Einstein condensation (BEC) of di-neutron pairs for both symmetric and neutron matter in the microscopic relativistic pairing theory. We take the bare nucleon-nucleon interaction Bonn-B in the particle-particle channel and the effective interaction PK1 of the relativistic mean-field approach in the particle-hole channel. It is found that the spatial structure of neutron Cooper pair wave function evolves continuously from BCS-type to BEC-type as density decreases. We see a strong concentration of the probability density revealed for the neutron pairs in the fairly small relative distance around $1.5 {\rm fm}$ and the neutron Fermi momentum $k_{Fn}\in[0.6,1.0] {\rm fm^{-1}}$. However, from the effective chemical potential and the quasiparticle excitation spectrum, there is no evidence for the appearance of a true BEC state of neutron pairs at any density. The most BEC-like state may appear at $k_{Fn}\thicksim0.2 {\rm fm^{-1}}$ by examining the density correlation function. From the coherence length and the probability distribution of neutron Cooper pairs as well as the ratio between the neutron pairing gap and the kinetic energy at the Fermi surface, some features of the BCS-BEC crossover are seen in the density regions, $0.05 {\rm fm^{-1}}<k_{Fn}<0.7 (0.75) {\rm fm^{-1}}$, for the symmetric nuclear (pure neutron) matter.

nucl-th↗

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.

nucl-th↗

arXiv2008

|Vub| from Exclusive Semileptonic B--> rho Decays

We use Omnes representations of the form factors V, A_1 and A_2 for exclusive semileptonic B--> rho decays, and apply them to combine experimental partial branching fraction information with theoretical calculations of the three form factors to extract |Vub|. We find a slightly lower result, |Vub|=(2.8 +- 0.2)x 10^{-3}, than the values extracted from exclusive semileptonic B-->pi decays and using all other inputs in CKM fits. The disagreement is greater when we compare to the result extracted from inclusive B -> X_u l nu decays.

hep-ph↗

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.

nucl-th↗

arXiv2007

Photon induced Lambda(1520) production and the role of the K^* exchange

We study the photon induced Lambda(1520) production in the effective Lagrangian method near threshold, E_γ^{LAB}<2 GeV, and in the quark-gluon string model at higher energies 3 GeV < E_γ^{LAB} < 5 GeV. In particular, we study the role of the K^* exchange for the production of Lambda(1520) within the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74 (2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^* pair, which is dynamically generated, turns out to be relatively small and, thus, the K exchange mechanism dominates the reaction. In the higher energy region, where experimental data are available, the quark-gluon string mechanism with the K Regge trajectory reproduces both the energy and the angular distribution dependences of the Lambda(1520) photo-production reaction.

hep-ph↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

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.

nucl-th↗

arXiv2006

Coleman-Weinberg mechanism for spontaneous chiral symmetry breaking in the massless chiral sigma model

We study the effect of one-loop corrections from nucleon together with those from boson in the massless chiral sigma model, where we perform the Coleman-Weinberg renormalization procedure. This renormalization procedure has a mechanism of spontaneous symmetry breaking due to radiative corrections in $ϕ^4$ theory. We apply it to the system of nucleon and bosons with chiral symmetry where the negative-mass term of bosons does not exist. Spontaneous chiral symmetry breaking is derived from the contribution of nucleon and boson loops which generates the masses of nucleon, scalar meson, and vector meson dynamically. We find that the renormalization scale plays an important role for the breaking of the symmetry between fermion (nucleon) and boson, and eventually for the chiral symmetry at the same time. In addition, we find that the naturalness restores by means of the introduction of the vacuum fluctuation from both nucleon and boson. Finally we obtain a stable effective potential with the effect of Dirac sea in the chiral model for the first time.

nucl-th↗