arXiv subjects

M. Yamamura

Publications and source records attributed to M. Yamamura.

At least 19 recordsLinked to original sources

arXiv2022

A possible trial beyond the conventional random phase approximation for the su(2)-Lipkin model including the case of non-closed shell system

Concerning the su(2)-Lipkin model, the calculation of the excitation energy to the 1st excited-state gives rise to the following fact: The two results based on the exact treatment and the conventional random phase approximation (RPA) are in unexpected disagreement. In order to remove this discrepancy, the conventional RPA is renewed. With the aim of this renewal, the terms, which cannot be dealt with in the conventional one, are estimated. The basic framework of this new form is not reorganized from that of the conventional one. In addition, the su(2)-Lipkin model itself is also modified so as to be applicable to the case with non-closed shell system. To this modification, one more su(2)-algebra, which has been already proposed by the present authors, is applied. Through the use of this algebra, the su(2)-Lipkin model is applicable to the case with any total fermion number permitted in the model.

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arXiv2020

Hybrid stars from a three-flavor NJL model with two kinds of tensor condensates

To obtain the equation of state of quark matter and construct hybrid stars, we calculate the thermodynamic potential in the three-flavor Nambu-Jona-Lasinio model including the tensor-type four-point interaction and the Kobayashi-Maskawa-'t Hooft interaction. To construct the hybrid stars, it is necessary to impose the beta-equilibrium and charge neutrality conditions on the system. It is shown that tensor condensed phases appear at large chemical potential. Under the possibility of the existence of the tensor condensates, the relationship between the radius and mass of hybrid stars is estimated.

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arXiv2020

Non-zero tensor condensates in cold quark matter within the three-flavor Nambu-Jona-Lasinio model with the Kobayashi-Maskawa-'t Hooft interaction

The possible formation of tensor condensates originated from a tensor-type interaction between quarks is investigated in the three-flavor Nambu-Jona-Lasinio model including the Kobayashi-Maskawa-'t Hooft interaction, which leads to flavor mixing. It is shown that independent two tensor condensates appear and a tensor condensate related to the strange quark easily occurs by the effect of the flavor mixing compared with one related to light quarks. Also, it is shown that the tensor condensate related to the strange quark appears at a slightly smaller chemical potential if the Kobayashi-Maskawa-'t Hooft interaction is included, due to the flavor mixing effect. It is also shown that the two kinds of tensor condensates may coexist in a certain quark chemical potential due to the flavor mixing.

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arXiv2020

Spin polarizations under a pseudovector interaction between quarks with the Kobayashi-Maskawa-'t Hooft term in high density quark matter

A possibility of a quark spin polarization originated from a pseudovector condensate is investigated in the three-flavor Nambu-Jona-Lasinio model with the Kobayashi-Maskawa-'t Hooft interaction which leads to flavor mixing. It is shown that a pseudovector condensate related to the strange quark easily occurs compared with pseudovector condensate related to light quarks. Further, it is shown that the pseudovector condensate related to the strange quark appears at a slightly small chemical potential by the effect of the flavor mixing due to the Kobayashi-Maskawa-'t Hooft interaction.

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arXiv2018

Hybrid stars from the NJL model with a tensor interaction

In order to obtain the equation of state and construct hybrid stars, we calculate the thermodynamic potential in the two-flavor Nambu--Jona-Lasinio model with tensor-type four-point interaction between quarks. In addition, we impose the beta equilibrium and charge neutrality conditions on the system. We show that the tensor condensate appears at large chemical potential, however, it is difficult to hold hybrid stars with two-solar mass by using the equation of state with the tensor interaction. Although we cannot obtain the stars with two-solar mass because of the absense of the repulsive interaction, the estimated magnetic moment density is very large. Therefore, we expect that the tensor interaction descrobes the magnetic fields of compact stars.

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arXiv2018

Spontaneous magnetization under a pseudovector interaction between quarks in high density quark matter

Spontaneous magnetization and magnetic susceptibility originated from the pseudovector-type four-point interaction between quarks are calculated in quark matter with zero temperature and finite quark chemical potential by using the two-flavor Nambu-Jona-Lasinio model. It is shown that both the chiral condensate and spin polarized condensate coexist in a narrow region of the quark chemical potential. And then, it is also shown that, in this narrow region, the spontaneous magnetization appears. Also, the magnetic susceptibility due to quarks with the positive energy is evaluated in the spin polarized phase.

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arXiv2017

A practical scheme for constructing the minimum weight states of the su(n)-Lipkin model in arbitrary fermion number

With the aim of performing an argument supplement to the previous paper by the present authors, in this paper, a practical scheme for constructing the minimum weight states of the su(n)-Lipkin model in arbitrary fermion number is discussed. The idea comes from the following two points : (i) consideration on the property of one-fermion transfer induced by the su(n)-generators in the Lipkin model and (ii) use of the auxiliary su(2)-algebra presented by the present authors. The form obtained under the points (i) and (ii) is simple.

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arXiv2017

Quark spin polarization and spontaneous magnetization in high density quark matter

By using the Nambu-Jona-Lasinio model with a tensor-type four-point interaction between quarks, it is shown that there exists a possibility of a spin polarized phase in quark matter at finite temperature and density. When there exists the spin polarization, the spontaneous magnetization may occur if the effect of the anomalous magnetic moment of quark is taken into account. An implication to the compact star objects with strong magnetic field is discussed when the spin polarization occurs.

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arXiv2017

A note on the Lipkin model in arbitrary fermion number

A possible form of the Lipkin model obeying the su(6)-algebra is presented. It is a natural generalization from the idea for the su(4)-algebra recently proposed by the present authors. All the relation appearing in the present form can be expressed in terms of the spherical tensors in the su(2)-algebras. For specifying the linearly independent basis completely, twenty parameters are introduced. It is concluded that, in these parameters, the ten denote the quantum numbers coming from the eigenvalues of some hermitian operators. The five in these ten determine the minimum weight state.

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arXiv2016

Spin Polarized versus Chiral Condensate in Quark Matter at Finite Temperature and Density

It is shown that the spin polarized condensate appears in quark matter at high baryon density and low temperature due to the tensor-type four-point interaction in the Nambu-Jona-Lasinio-type model as a low energy effective theory of quantum chromodynamics. It is indicated within this low energy effective model that the chiral symmetry is broken again by the spin polarized condensate as increasing the quark number density, while the chiral symmetry restoration occurs in which the chiral condensate disappears at a certain density.

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arXiv2015

Spontaneous magnetization in high-density quark matter

It is shown that the spontaneous magnetization occurs due to the anomalous magnetic moments of quarks in the high-density quark matter under the tensor-type four-point interaction. The spin polarized condensate for each flavor of quark appears at high baryon density, which leads to the spontaneous magnetization due to the anomalous magnetic moments of quarks. The implications to the strong magnetic field in the compact stars is discussed.

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arXiv2015

A possibility of quark spin polarized phase in high density quark matter

It is shown that the quark spin polarization may occur for each quark flavor by the use of the Nambu-Jona-Lasinio model with a tensor-type four-point interaction between quarks, while the two-flavor color superconducting phase in two-flavor case may be realized at high density quark matter.

hep-ph↗

arXiv2015

New boson realization of the Lipkin model obeying the su(2)-algebra

New boson representation of the su(2)-algebra proposed by the present authors for describing the damped and amplified oscillator is examined in the Lipkin model as one of simple many-fermion models. This boson representation is expressed in terms of two kinds of bosons with a certain positive parameter. In order to describe the case of any fermion number, third boson is introduced. Through this examination, it is concluded that this representation is well workable for the boson realization of the Lipkin model in any fermion number.

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arXiv2014

Spin Polarization versus Color-Flavor-Locking in High Density Quark Matter

It is shown that spin polarization with respect to each flavor in three-flavor quark matter occurs instead of the color-flavor locking at high baryon density by using the Nambu-Jona-Lasinio model with four-point tensor-type interaction. Also, it is indicated that the order of phase transition between the color-flavor locked phase and the spin polarized phase is the first order by means of the second order perturbation theory.

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arXiv2013

Interplay between Spin Polarization and Color Superconductivity in High Density Quark Matter

Here, it is suggested that a four-point interaction of the tensor type may lead to spin polarization in quark matter at high density. It is found that the two-flavor superconducting phase and the spin polarized phase correspond to distinct local minima of a certain generalized thermodynamical potential. It follows that the transition from one to the other phase occurs passing through true minima with both a spin polarization and a color superconducting gap. It is shown that the quark spin polarized phase is realized at rather high density, while the two-flavor color superconducting phase is realized at a lower density region.

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arXiv2013

A Pseudo su(1,1)-Algebraic Deformation of the Cooper-Pair in the su(2)-Algebraic Many-Fermion Model

A pseudo su(1,1)-algebra is formulated as a possible deformation of the Cooper-pair in the su(2)-algebraic many-fermion system. With the aid of this algebra, it is possible to describe behavior of individual fermions which are generated as the result of interaction with the external environment. The form presented in this paper is a generalization of a certain simple case developed recently by the present authors. Basic idea follows the su(1,1)-algebra in the Schwinger boson representation for treating energy transfer between the harmonic oscillator and the external environment. Hamiltonian is given under the idea of the phase space doubling in the thermo-field dynamics formalism and the time-dependent variational method is applied to this Hamiltonian. Its trial state is constructed in the frame deformed from the BCS-Bogoliubov approach to the superconductivity. Several numerical results are shown.

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arXiv2012

Quark-Hadron Phase-Transition in an Extended NJL Model with Scalar-Vector Interaction

The quark-hadron phase transition at finite temperature and baryon chemical potential is investigated in an extended NJL model with scalar-vector eight-point interaction by comparing the pressure of symmetric nuclear matter with that of the quark matter. As a result, the extended NJL phase diagram is obtained in the temperature-baryon chemical potential plane and the effects of the scalar-vector coupling constant G_{sv}^q on the chiral phase transition are summarized. It is shown that a quarkyonic-like phase in which the chiral symmetry is restored but the elementary excitation modes are nucleonic appears just before deconfinement in this model.

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arXiv2012

Effective Potential Approach to Quark Ferromagnetization in High Density Quark Matter

A possibility of spontaneous magnetization in high density symmetric quark matter is investigated using the NJL type effective model of QCD by means of an effective potential with respect to an auxiliary field. It is shown that the quark ferromagnetic condensate has non-vanishing value at high baryon density due to the tensor-type four-point interaction between quarks.

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