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Y. Tsue

Publications and source records attributed to Y. Tsue.

At least 37 records · Page 2Linked to original sources
arXiv2012

The BCS-Bogoliubov and the su(2)-Algebraic Approach to the Pairing Model in Many-Fermion System

The relation between two approaches to the su(2)-algebraic many-fermion model is discussed: (1) the BCS-Bogoliubov approach in terms of the use of the quasiparticles representing all the degrees of freedom except those related to the Cooper-pairs and (2) the conventional algebraic approach in terms of the use of the minimum weight states, from which the Cooper-pairs are excluded. In order to arrive at the goal, the idea of the quasiparticles is brought up in the conservation of the fermion number. Under the c-number replacement for the three su(2)-generators, the quasiparticles suggested in this paper are reduced to those in the BCS-Bogoliubov approach. It is also shown that the two approaches are equivalent through the c-number replacement. Further, a certain modification of the BCS-Bogoliubov approach is discussed.

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arXiv2012

A Role of the Quasiparticle in the Conservation of the Fermion Number

The role of the "quasiparticle" introduced in last paper by the present authors is discussed. It serves as a guide for the deformation of the Cooper-pair in the BCS-Bogoliubov approach. As an illustrative example, a certain case is treated. This case produces the su(1,1)-like behavior in the su(2)-algebraic many-fermion system.

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arXiv2012

Scalar and Pseudoscalar Glueball Masses within a Gaussian Wavefunctional Approximation

The lowest scalar and pseudoscalar glueball masses are evaluated by means of the time-dependent variational approach to the Yang-Mills gauge theory without fermions in the Hamiltonian formalism within a Gaussian wavefunctional approximation. The glueball mass is calculated as a pole of the propagator for a composite glueball field which consists of two massless gluons. The glueball propagator is here evaluated by using the linear response theory for the composite external glueball field. As a result, a finite glueball mass is obtained through the interaction between two massless gluons, in which the glueball mass depends on the QCD coupling constant g in the nonperturbative form.

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arXiv2012

Color-Singlet Three-Quark States in the su(4)-Algebraic Many-Quark Model

As announced in last paper by the present authors, the color-singlet three-quark states are investigated for the case of the spherical j-j coupling and L-S coupling shell models. The latter case automatically leads to the su(4)*su(4)-model. For a certain type of Hamiltonian, the states of individual "nucleons" are characterized.

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arXiv2011

Note on the Minimum Weight States in the su(2)-Algebraic Many-Fermion Model --- Extension of the Role of the Auxiliary su(2)-Algebra ---

The role of the auxiliary su(2)-algebra proposed by the present authors in the latest paper is extended. Its aim is to determine the minimum weight states completely. With the aid of scalar operators for the auxiliary algebra, new aspects are added to the minimum weight states in the aligned scheme discussed in the latest paper. Some simple examples are shown.

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arXiv2011

Background of the su(2)-Algebraic Many-Fermion Models in the Boson Realization

The su(2)-algebraic many-fermion model is formulated so as to be able to get the unified understanding of the structures of three simple models: the single-level pairing, the isoscalar proton-neutron pairing and the two-level Lipkin model. Basic idea is to introduce an auxiliary su(2)-algebra, any generator of which commutes with any generator of the starting su(2)-algebra. With the aid of this algebra, the minimum weight states are completely determined in a simple forms. Further, concerning the two algebras, boson realization is presented. Through this formulation, the behavior of the total fermion in the Lipkin model is notably different of those in the other two models. As supplementary problem, the boson-fermion realization and the Lipkin model in the isovector pairing model are investigated.

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arXiv2011

On the Color-Singlet States in Many-Quark Model with the su(4)-Algebraic Structure. II

Ground-state energies are investigated in a many-quark model with pairing interactions, which has the su(4)-algebraic structure. Exact eigenstates in the boson realization method are constructed by imposing a color-singlet condition developed in the previous paper. An interaction term breaking the su(4)-dynamical symmetry plays an important role to determine the ground state. As a result, a quark-pairing state or a quark-triplet state as a nucleon is realized with a certain value of a variable which is regarded as an order parameter. In addition to the parameter regions in which these ground states are realized, it is shown that there are two transition regions between the quark-pairing and the quark-triplet states with different values of the order parameter.

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arXiv2011

On the Color-Singlet States in Many-Quark Model with the su(4)-Algebraic Structure. III

A phase structure and phase transitions are investigated in the modified Bonn quark model. The force strength, which represents the particle-hole type interaction, is devised so as to depend on the quark number, namely quark number density. As a result, it is shown that the phase transition from the quark-triplet state as a nucleon to the quark-pair state as a color-superconducting state occurs as the density increases.

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arXiv2010

Two-Level Lipkin Model in Unconventional Boson Realization

With the aim of applying to the Lipkin model in the case of open shell system, a possible form of the boson realization for the su(2)-algebra is proposed both in the Schwinger and the Holstein-Primakoff representation. The basic idea is borrowed from the Schwinger boson realization for the su(4)-algebra for many-quark system recently presented by the present authors. As the simplest approximation, a certain approximate form is given and the result is a natural generalization of the RPA result in the case of closed shell system.

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arXiv2010

First Order Quark-Hadron Phase Transition in the NJL-Type Nuclear and Quark Model

The quark-hadron phase transition at finite baryon chemical potential is investigated in the extended Nambu-Jona-Lasinio model in which the scalar-vector eight-point interaction is included holding the chiral symmetry. By comparing a pressure of the symmetric nuclear matter with that of the quark matter, the realized phase at given baryon density is determined. As a result, the first order quark-hadron phase transition is derived where the deconfinement transition occurs after the chiral symmetry restoration in this model.

hep-ph↗
arXiv2009

Note on Many-Quark Model with su(4) Algebraic Structure

In a many-quark model developed in our previous paper where two-body color pairing and particle-hole type interactions are active, the exact energy eigenstates are re-formed with physically clearer expressions than those derived in our previous paper. By using the re-formed energy eigenstates, two types of the eigenstates in which the pairing correlation and the quark triplet formation separately appear definitely, are unified and this model can be treated for both the strong color correlations and the quark triplet formations.

hep-ph↗
arXiv2009

On the Exact Eigenstates and the Ground States Based on the Boson Realization for Many-Quark Model with su(4) Algebraic Structure

Based on the boson realization, the ground state and phase structure are investigated in a many-quark model with algebraic structure developed in our previous paper, in which the two-body pairing and particle-hole type interactions are active. The physical interpretation of the exact eigenstates obtained in the boson realization in our previous paper is given in a many-quark model with su(4) algebraic structure.

hep-ph↗
arXiv2009

Time-Dependent Variational Approach to the Non-Abelian Pure Gauge Theory

The time-dependent variational approach to the pure Yang-Mills gauge theory, especially a color su(3) gauge theory, is formulated in the functional Schroedinger picture with a Gaussian wave functional approximation. The equations of motion for the quantum gauge fields are formulated in the Liouville-von Neumann form. This variational approach is applied in order to derive the transport coefficients, such as the shear viscosity, for the pure gluonic matter by using the linear response theory. As a result, the contribution to the shear viscosity from the quantum gluons is zero up to the lowest order of the coupling g in the quantum gluonic matter.

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arXiv2008

Variational Approach to the Chiral Phase Transition in the Linear Sigma Model

The chiral phase transition at finite temperature is investigated in the linear sigma model, which is regarded as a low energy effective theory of QCD with three momentum cutoff, in the variational method with the Gaussian approximation in the functional Schroedinger picture. It is shown that the Goldstone theorem is retained and the meson pair excitations are automatically included by taking into account the linear response to the external fields. It is pointed out that the behavior of chiral phase transition depends on the three-momentum cutoff, which leads to the careful treatment of the problem.

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arXiv2008

Many-Quark Model with su(4) Algebraic Structure

With the use of a certain type of the Schwinger boson representation of the su(4) algebra, the Bonn model for many-quark systems and an extension of the model, in which the energies of the various exact states are controled, namely, the energies are enhanced or de-enhanced, are investigated. Especially, the triplet formation and the pairing correlation in many-quark states are discussed. In the boson space, all the results are analytically expressed in the exact forms.

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arXiv2007

Amplification of Quantum Meson Modes in the Late Time of the Chiral Phase Transition

We investigate the time evolution of the quantum meson modes in the late time of chiral phase transition. In particular, it is shown that there exists a possible solution to the equation of motion for the quantum meson modes, which reveals a parametric resonance and/or resonance through forced oscillation induced by the small oscillation of the chiral condensate. After that, we demonstrate the unstable regions for the quantum meson modes in both the cases of a uniform and spatially expanding system.

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