arXiv subjects

Shun-ichiro Koh

Publications and source records attributed to Shun-ichiro Koh.

13 recordsLinked to original sources

arXiv2026

Massive gauge boson and Higgs boson as the vestiges of non-Fock vacuum

A microscopic model of the Brout-Englert-Higgs (BEH) mechanism is proposed. Massless fermions and antifermions do not belong to the Fock space with definite particle-number distribution, but belong to a non-Fock space with indefinite one. From this vast space, their ground-state is selected by a kinematical condition. Due to the interaction between them, the Fock state in which fermions and antifermions are massive is restored, but this state has the vestiges of the non-Fock state in the massive gauge boson and the Higgs boson. In the non-Fock state, massless fermions and antifermions exist as pairs, and behave as quasi bosons within a small space-time region. Due to Bose statistics, the direction of their center-of-mass motion is parallel to each other, and their transverse excitations are suppressed by an energy gap, making the gauge boson coupled to them massive. The Higgs boson is not an elementary particle, but a quasiparticle appearing after the Fock vacuum is restored.

physics.gen-ph↗

arXiv2023

Space-time approach to spontaneous symmetry breaking in the Abelian-gauge interaction

Spontaneous symmetry breaking is examined by regarding it as a phenomenon in the eternal intermediate state due to sequential perturbations. The concept of the relativistic many-body state is applied to this intermediate state occurring in the collision of massless Dirac fermions. Time in the relativistic many-body state should evolve while maintaining the direction of time in each particle, even if the particles are viewed from any inertial frames. This kinematical requirement leads to spontaneous symmetry breaking in the vacuum of these states, which gives a different meaning to the results of the Higgs model. In this vacuum, massless fermion-antifermion pairs and coherent collection of gauge bosons condense, which determine each other's mass. When a local excitation of the condensed gauge bosons propagates in space, a Higgs-like boson appears. The effective coupling of this Higgs-like boson to gauge bosons is calculated as a one-loop process. With this coupling, the total cross section of the pair annihilation of fermion and antifermion to gauge boson pair is calculated. Renormalizability of this model is discussed using the inductive method. Since the Higgs Lagrangian is not assumed, the divergence we must renormalize is only the logarithmic divergence, not the quadratic one.

hep-th↗

arXiv2018

Spectral Analysis of the Growth of Translational Superfluid Flow in a Bose Liquid

Spectral analysis of the translational superfluid flow of a Bose liquid is attempted. When cooling a dissipative flow of liquid helium 4 through a capillary at the lambda temperature,a superfluid flow abruptly appears at the lambda temperature. By a thought experiment in which the pressure difference between two ends of a capillary slowly oscillates, the spectrum of fluidity (the reciprocal of kinematic viscosity) just above the lambda temperature ($2.17 K<T<2.18 K$) is examined using a sum rule that incorporates the result of linear response theory and fluid mechanics. According to Feynman's picture on the many-body wave function of bosons, as the condensate grows in the flow, the transverse motion in the flow becomes suppressed by the emergence of a gap, originating from the Bose statistics, in the excitation spectrum. This statistical gap induces a continuous change in the fluidity spectrum just above the lambda temperature, which demonstrates the growth of a superfluid flow. For this mechanism, the size distribution of the coherent wave function plays an important role. As a byproduct, a new interpretation of the critical velocity is proposed.

cond-mat.stat-mech↗

arXiv2010

Dynamics of Superflow by Mesoscopic Condensate

The shear viscosity $η$ of a quantum liquid in the vicinity of $T_λ$ is examined. In liquid helium 4 above $T_λ$ ($T_λ<T<3.7K$), under a strong effect of Bose statistics, the coherent many-body wave function grows to an intermediate size between a macroscopic level and a microscopic one. These wave functions are qualitatively different from thermal fluctuation, and manifest themselves in the gradual decrease in shear viscosity above $T_λ$. To formulate this phenomenon, we combine the correlation function with fluid dynamics. Applying the Kramers-Kronig relation to the generalized Poiseuille's formula for capillary flow, we perform a perturbation calculation of the reciprocal $1/η$ with respect to the particle interaction, and examine how the growth of coherent wave functions gradually decreases shear viscosity. Comparing with the experimentally determined $η(T)$, $\hat {ρ\cdot}_s(T)/ρ\cdot$ of such a mesoscopic condensate is estimated to reach $10^{-5}$ just above $T_λ$. We examine the effect of condensate size on the stability of such a superflow, and touch upon the superflow in porous media.

cond-mat.other↗

arXiv2008

The onset of superfluidity in capillary flow of liquid helium 4

The onset mechanism of superfluidity is examined by taking the case of the capillary flow of liquid helium 4. In the capillary flow, a substantial fall of the shear viscosity has been observed in the normal phase (lambda point<T<3.7K). In this temperature region, under the strong influence of Bose statistics, the coherent many-body wave function grows to an intermediate size between a macroscopic and a microscopic one, which is different from thermal fluctuation. We consider such a capillary flow by including it to a general picture that includes the flow of rotating helium 4 as well. Using the Kramers-Kronig relation, we express the inverse of the shear viscosity in terms of the generalized susceptibility of the system, and obtain a formula for the shear viscosity in the vicinity of the lambda point. Regarding bosons without the condensate as a non-perturbative state, we make a perturbation calculation of the susceptibility with respect to the repulsive interaction. With decreasing temperature from 3.7K, the growth of the coherent wave function gradually suppresses the shear viscosity, and makes the superfluid flow stable. Comparing formulas obtained to the experimental data, we estimate that the ratio of the superfluid density defined in the mechanical sense reaches 1/100000 just above the lambda point.

cond-mat.supr-con↗

arXiv2007

Shear viscosity of liquid helium 4 above the lambda point

In liquid helium 4, many features associated to Bose statistics have been masked by the strongly interacting nature of the liquid. As an example of these features, we examine the shear viscosity of liquid helium 4 above the lambda point. Applying the linear-response theory to Poiseuille's formula for the capillary flow, the reciprocal of the shear viscosity coefficient is considered as a transport coefficient. Using the Kramers-Kronig relation, we relate a superfluid flow in a capillary with that in a rotating bucket, and express the reciprocal of the shear viscosity coefficient in terms of the susceptibility of the system. A formula for the kinematic shear viscosity is obtained which describes the influence of Bose statistics. Using this formula, we study the gradual fall of the kinematic shear viscosity from 3.7K to the lambda point in liquid helium 4 at 1 atm.

cond-mat.supr-con↗

arXiv2007

Meissner effect in a charged Bose gas with short-range repulsion

The question of whether the BEC is a necessary condition of the Meissner effect is examined. The electromagnetic susceptibility of a charged Bose gas with short-range repulsion is studied using the perturbation theory with respect to the repulsive force. With decreasing temperature, the Bose-statistical coherence grows, and prior to the BEC phase the susceptibility shows a singularity implying the Meissner effect. This means that the BEC is a sufficient, but not a necessary condition of the Meissner effect in the charged Bose gas with short-range repulsion.

cond-mat.supr-con↗

arXiv2007

Quantum gas-liquid condensation in an attractive Bose gas

Gas-liquid condensation (GLC) in an attractive Bose gas is studied on the basis of statistical mechanics. Using some results in combinatorial mathematics, the following are derived: (1) With decreasing temperature, the Bose-statistical coherence grows in the many-body wave function, which gives rise to the divergence of the grand partition function prior to Bose-Einstein condensation. It is a quantum-mechanical analogue to the GLC in a classical gas (quantum GLC). (2) This GLC is triggered by the bosons with zero momentum. Compared with the classical GLC, an incomparably weaker attractive force creates it. For the system showing the quantum GLC, we discuss a cold helium 4 gas at sufficiently low pressure.

cond-mat.stat-mech↗

arXiv2007

Nonclassical rotational behavior at the vicinity of the lamda point

The rotational property of a quantum liquid at the vicinity of the lambda point is examined. In a liquid helium 4 just above the lambda point, under the strong influence of Bose statistics, the coherent many-body wave function grows to an intermediate size between a macroscopic and a microscopic one, which is of a different nature from the thermal fluctuations. It must reflect in the rotational properties such as the moment of inertia. Beginning with the bosons without the condensate, we make a perturbation calculation of its susceptibility with respect to the repulsive interaction, and examine how, with decreasing temperature, the growth of the coherent wave function gradually changes the rotational behavior of a liquid:The moment of inertia slightly decreases just above the lambda point. This means that at the vicinity of the lambda point, the mechanical superfluid density does not always agree with the thermodynamical one.We compare the result to the experiment by Hess and Fairbank. A new interpretation of the shear viscosity just above the lambda point is given from this viewpoint.

cond-mat.supr-con↗

arXiv2007

Shear viscosity and Bose statistics: Capillary flow above lambda point

The gradual fall of the shear viscosity below 2.8K, observed in a liquid helium 4 flowing through a capillary, is examined. The disappearance of the shear viscosity in a capillary flow is a manifestation of superfluidity in dissipative phenomena, the onset mechanism of which is a subtle problem compared to that of superfluidity in non-dissipative phenomena. Applying the linear-response theory to the reciprocal of the shear viscosity coefficient, we relate these two types of superfluidity using the Kramers-Kronig relation. We obtain a formula describing the influence of Bose statistics on the kinematic shear viscosity in terms of the susceptibility. Compared to an ordinary liquid, a liquid helium 4 above the lambda point has a 1/1000 times smaller shear viscosity coefficient. Hence, although in the normal phase, it is already an anomalous liquid under the strong influence of Bose statistics. The coherent many-body wave function grows to an intermediate size between a macroscopic and a microscopic one, not as a thermal fluctuation but as a thermal equilibrium state. Beginning with bosons without the condensate, we make a perturbation calculation of its susceptibility with respect to the repulsive interaction. We examine how, with decreasing temperature, the growth of the coherent wave function gradually suppresses the shear viscosity, and finally leads to a frictionless flow at the lambda-point.

cond-mat.supr-con↗

arXiv2004

Non-classical rotational inertia in the supersolid state

An abrupt drop in the moment of inertia recently found in solid helium 4 is explained in terms of dynamics of zero-point vacancies (ZPV). Mechanical decoupling of ZPV from the motion of the container due to Bose statistics is developed to a macroscopic phenomenon by repulsive interaction. It gives a negative answer to the question whether BEC is a necessary condition for non-classical rotational inertia in a bulk three-dimensional system.

cond-mat.stat-mech↗

arXiv2002

An interpretation of the black-body radiation

The black-body radiation is reinterpreted in terms of the photon's many-body wave functions in analogy with the condensed matter physics. This interpretation has implications on the wave-particle duality, and on the difference between the photon and the matter wave.

quant-ph↗

arXiv2000

Attractive Boson and the Gas-Liquid Condensation

We calculate a grand partition function of the attractive Bose gas in the infinite space within some approximations. Using the idea of the Yang-Lee zeros, it is proved that the gas-liquid condensation occurs before the conventional condition of the Bose-Einstein condensation is satisfied. Further, it is pointed out that Bosons with a zero momentum play a role of a trigger to this gas-liquid condensation. We discuss its implication to the trapped atomic gas.

cond-mat↗