論文 - 青木　健一郎

Fluctuation spectroscopy of surface melting of ice with and without impurities

Mitsui T., Aoki K.

Physical Review E （Physical Review E）  99 （ 1 ）  2019年01月

ISSN  24700045

　概要を見る

© 2019 American Physical Society. Water is ubiquitous, and the surface properties of ice have been studied for some time, due to their importance. A liquidlike layer (LLL) is known to exist on ice, below the melting point. We use surface thermal fluctuation spectroscopy to study the LLL, including its thickness, for pure ice, and for ice with impurities. We find that the properties of the LLL are experimentally those of liquid water, with thickness much smaller than previous results. We also find that impurities cause the LLL to be thicker, and quite inhomogeneous, with properties depending on the dopant.

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Dynamically enhanced low-coherence interferometry

Mitsui T., Aoki K.

Review of Scientific Instruments （Review of Scientific Instruments）  89 （ 9 ）  2018年09月

ISSN  00346748

　概要を見る

© 2018 Author(s). In the investigations of inhomogeneous media, availability of methods to study the interior of the material without affecting it is valuable. Optical coherence tomography provides such a functionality by providing depth resolved images of semi-transparent objects non-invasively. This is especially useful in medicine and is used not only in research but also in clinical practice. Optical coherence tomography characterizes each cross section by its reflectance. The basic physics principle underlying optical coherence tomography is low-coherence interferometry, which is combined with lateral scanning to produce cross sections. It is clearly desirable to obtain more detailed information regarding each cross section, if available. We have developed a system which measures the fluctuation spectra at all depths in low-coherence interferometry. By providing more information for each cross section, this can in principle be effective in tissue characterization and pathological diagnosis. The system uses the time dependence of the low-coherence interferometry data to obtain the fluctuation spectrum at each depth. Additionally, noise reduction is applied to obtain the spectra without unwanted noise, such as shot-noise, which can swamp the signal. The measurement system is applied to samples with no external stimuli, and depth resolved thermal fluctuation spectra of the samples are obtained. These spectra are compared with their corresponding theoretical expectations and are found to agree. The measurement system requires dualizing the detectors in the low-coherence interferometer but otherwise requires little additional equipment. The measurements were performed in ten to a hundred seconds.

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Thermal interface fluctuations of liquids and viscoelastic materials

Aoki K., Mitsui T.

Progress of Theoretical and Experimental Physics （Progress of Theoretical and Experimental Physics）  2018 （ 4 ）  2018年04月

ISSN  2050-3911

　概要を見る

© 2018 Physical Society of Japan. All rights reserved. Spectra of thermal fluctuations of a wide range of interfaces, from liquid/air, viscoelastic material/ air, liquid/liquid to liquid/viscoelastic material interfaces, were measured over a 100 Hz to 10MHz frequency range. The obtained spectra were compared with the fluctuation theory of interfaces, and found to be mostly in quite good agreement, when the theory was generalized to apply to thermal fluctuations of liquid/viscoelastic material interfaces. The loss modulus of viscoelastic materials has been incorporated into the theory, and its effects observed experimentally. The spectra were measured using a system that combines light reflection, statistical noise reduction through averaged correlations, and confocal microscopy. It requires only a small area of the interface (∼1μm2), relatively short times for measurements (≲ few min), and can also be applied to highly viscous materials.

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Order and chaos in the one-dimensional ϕ⁴ model: N-dependence and the Second Law of Thermodynamics

Hoover W., Aoki K.

Communications in Nonlinear Science and Numerical Simulation （Communications in Nonlinear Science and Numerical Simulation）  49   192 - 201 2017年08月

ISSN  10075704

　概要を見る

© 2017 Elsevier B.V. We revisit the equilibrium one-dimensional ϕ4 model from the dynamical systems point of view. We find an infinite number of periodic orbits which are computationally stable. At the same time some of the orbits are found to exhibit positive Lyapunov exponents! The periodic orbits confine every particle in a periodic chain to trace out either the same or a mirror-image trajectory in its two-dimensional phase space. These “computationally stable” sets of pairs of single-particle orbits are either symmetric or antisymmetric to the very last computational bit. In such a periodic chain the odd-numbered and even-numbered particles’ coordinates and momenta are either identical or differ only in sign. “Positive Lyapunov exponents” can and do result if an infinitesimal perturbation breaking a perfect two-dimensional antisymmetry is introduced so that the motion expands into a four-dimensional phase space. In that extended space a positive exponent results. We formulate a standard initial condition for the investigation of the microcanonical chaotic number dependence of the model. We speculate on the uniqueness of the model's chaotic sea and on the connection of such collections of deterministic and time-reversible states to the Second Law of Thermodynamics.

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Observation of reflectance fluctuations in metals

Mitsui T., Aoki K.

Physical Review A （Physical Review A）  95 （ 4 ）  2017年04月

ISSN  24699926

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© 2017 American Physical Society. Through the study of the power spectra of a monochromatic light beam reflected by metallic mirrors, fluctuations in their reflectance are observed. The power spectra were obtained down to a factor 10-6 below the standard quantum limit, with a dynamic range of 105 in frequency and power, using methods we developed. The properties of the spectra are investigated, and their dependence on the material is analyzed. The physics underlying the phenomenon is also discussed. These fluctuations provide a window into the degrees of freedom responsible for the reflection process in metals.

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Stable and unstable periodic orbits in the one-dimensional lattice φ4 theory

Aoki K.

Physical Review E （Physical Review E）  94 （ 4 ）  2016年10月

ISSN  24700045

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© 2016 American Physical Society. Periodic orbits for the classical φ4 theory on the one-dimensional lattice are systematically constructed by extending the normal modes of the harmonic theory, for periodic, free and fixed boundary conditions. Through the process, we investigate which normal modes of the linear theory can or cannot be extended to the full nonlinear theory and why. We then analyze the stability of these orbits, clarifying the link between the stability, parametric resonance, and Lyapunov spectra for these orbits. The construction of the periodic orbits and the stability analysis is applicable to theories governed by Hamiltonians with quadratic intersite potentials and a general on-site potential. We also apply the analysis to theories with on-site potentials that have qualitatively different behavior from the φ4 theory, with some concrete examples.

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Observing random walks of atoms in buffer gas through resonant light absorption

Aoki K., Mitsui T.

Physical Review A （Physical Review A）  94 （ 1 ）  2016年07月

ISSN  24699926

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© 2016 American Physical Society. Using resonant light absorption, random-walk motions of rubidium atoms in nitrogen buffer gas are observed directly. The transmitted light intensity through atomic vapor is measured, and its spectrum is obtained, down to orders of magnitude below the shot-noise level to detect fluctuations caused by atomic motions. To understand the measured spectra, the spectrum for atoms performing random walks in a Gaussian light beam is computed, and its analytical form is obtained. The spectrum has 1/f2 (f is frequency) behavior at higher frequencies, crossing over to a different, but well-defined, behavior at lower frequencies. The properties of this theoretical spectrum agree excellently with the measured spectrum. This understanding also enables us to obtain the diffusion constant, the photon cross section of atoms in buffer gas, and the atomic number density from a single spectral measurement. We further discuss other possible applications of our experimental method and analysis.

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Noise reduction and hyperfine level coherence in spontaneous noise spectroscopy of atomic vapor

Mitsui T., Aoki K.

Journal of the Optical Society of America B: Optical Physics （Journal of the Optical Society of America B: Optical Physics）  31 （ 2 ） 195 - 200 2014年02月

ISSN  07403224

　概要を見る

We developed a system for measurements of power spectra of transmitted light intensity fluctuations, in which the extraneous noise, including shot noise, is reduced. In essence, we just apply light, measure the power of the transmitted light, and derive its power spectrum. We use this to observe the spontaneous noise spectra of photon atom interactions. Applying light with frequency modulation, we can also observe the spontaneous noise reflecting the coherence between the hyperfine levels in the excited state. There are two main novel components in the measurement system, the noise reduction scheme and the stabilization of the laser system. The noise reduction mechanism can be used to reduce the shot noise contribution to arbitrarily low levels through averaging, in principle. This is combined with differential detection to keep unwanted noise at low levels. The laser system is stabilized to obtain spectral width below 1 kHz without high frequency (≳10 MHz) noise. These methods are described systematically and the performance of the measurement system is examined through experimental results. © 2014 Optical Society of America.

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Observation of spontaneous quantum fluctuations in photon absorption by atoms

Mitsui T., Aoki K.

European Physical Journal D （European Physical Journal D）  67 （ 10 ）  2013年12月

ISSN  14346060

　概要を見る

Fluctuations in light absorption by atoms are observed by applying laser light on rubidium atoms and measuring the transmitted light intensity fluctuations. These fluctuations are spontaneous noise, generic to photon atom interactions. By making use of the sub-shot noise random signal detection technology, we have measured the spectra at sub-shot noise levels to reveal their rich nature, whose whole structure had previously been unobserved. The effects of atoms transiting the laser beam, Rabi flopping in the optical transitions and Larmor precession of the magnetic moment are observed in the spectra. The properties of the fluctuations reflect not only the quantum behavior of atoms but also that of light. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2013.

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Measurements of liquid surface fluctuations at sub-shot-noise levels with Michelson interferometry

Mitsui T., Aoki K.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics （Physical Review E - Statistical, Nonlinear, and Soft Matter Physics）  87 （ 4 ）  2013年04月

ISSN  15393755

　概要を見る

Surface fluctuation spectra of liquids are measured to unprecedented precision, down to 3 orders of magnitude below the shot-noise level using averaged correlations of interferometry measurements. This allows us to investigate the limits in our current theoretical understanding of these phenomena. The spectrum derived from hydrodynamical considerations agrees well with the observed results for water. However, for oil, deviations are seen at high frequencies (1 MHz), perhaps indicating its more complex underlying physics. The measurements are made possible by dualizing the Michelson interferometry measurements and employing the averaged correlation of signals, in which the shot noise is statistically reduced. The method works in the presence of the quantum noise of a coherent state of light. The optical part of the experimental setup is essentially the same as that of Michelson interferometry so that the method can be applied when Michelson interferometry can be used. Furthermore, the measurement method requires a relatively low light power and a short time so that it has a wide range of applicability. © 2013 American Physical Society.

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Direct observations of thermal fluctuations below shot noise levels

青木 健一郎，三井 隆久

素粒子論研究 13 （ 4 ）  2013年

研究論文（学術雑誌）, 共著

Michelson interferometry with quantum noise reduction

三井 隆久，青木 健一郎

Physical Review E87   042403 2013年

研究論文（学術雑誌）, 単著, 査読有り

Spectral properties of thermal fluctuations on simple liquid surfaces below shot-noise levels

青木 健一郎，三井 隆久

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics （Physical Review E - Statistical, Nonlinear, and Soft Matter Physics）  E86 （ 1 ） 011602 2012年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  15393755

　概要を見る

We study the spectral properties of thermal fluctuations on simple liquid surfaces, sometimes called ripplons. Analytical properties of the spectral function are investigated and are shown to be composed of regions with simple analytic behavior with respect to the frequency or the wave number. The derived expressions are compared to spectral measurements performed orders of magnitude below shot-noise levels, which is achieved using a novel noise reduction method. The agreement between the theory of thermal surface fluctuations and the experiment is found to be excellent, elucidating the spectral properties of the surface fluctuations. The measurement method requires relatively only a small sample both spatially (few μm) and temporally (∼20s). The method also requires relatively weak light power (∼0.5mW) so that it has a broad range of applicability, including local measurements, investigations of time-dependent phenomena, and noninvasive measurements. © 2012 American Physical Society.

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Direct optical observations of surface of thermal motions at sub-shot noise levels

青木 健一郎,三井隆久

Physical Review E80   020602(R)-1-4 2009年

研究論文（学術雑誌）, 共著, 査読有り

A tabletop experiment for the direct measurement of the speed of light

Aoki K., Mitsui T.

American Journal of Physics （American Journal of Physics）  76 （ 9 ） 812 - 815 2008年09月

ISSN  00029505

　概要を見る

We describe a tabletop experiment for the direct measurement of the speed of light to an accuracy of a few percent. The experiment is accessible to students not majoring in science or engineering. The experiment can include a measurement of the index of refraction of a sample. We discuss the experimental apparatus and safety considerations. The results and limitations of the experiment are analyzed, based partly on our experience in employing the experiment in student laboratories. © 2008 American Association of Physics Teachers.

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Some thermal transport properties of the FPU model with quadratic pinning

青木 健一郎

Progress of Theoretical Physics （Progress of Theoretical Physics）  119 （ 119 ） 717-724 - 724 2008年

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  0033068X

　概要を見る

Thermal transport properties of the FPU β model with a quadratic pinning term are investigated for various couplings and temperatures. In particular, the size dependence of the thermal conductivity, κ α Lα, is studied. α agrees with that of the FPU β model (with no pinning) at high temperatures but decreases at low temperatures. This crossover behavior occurs at a temperature depending on the strength of the quadratic pinning.

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A small tabletop experiment for a direct measurement of the speed of light

青木 健一郎

American Journal of Physics  （ 76 ） 812-815 2008年

研究論文（学術雑誌）, 共著, 査読有り

Momentum cumulants, local equilibrium and stochastic thermostats

青木 健一郎

Physics Letters, Section A: General, Atomic and Solid State Physics （Physics Letters, Section A: General, Atomic and Solid State Physics）  368 （ A368 ） 77 - 81 2007年

研究論文（学術雑誌）, 単著, 査読有り,  ISSN  03759601

　概要を見る

We quantitatively investigate the behavior of momentum cumulants in the φ{symbol}4 theory under thermal gradients, using stochastic thermostats. We relate this to the violations of local equilibrium. The non-equilibrium behavior is found to be quite well described by a dependence ∼ (∇ T)2, on the temperature gradient. Dependence of the quantities on the thermostat type is analyzed and its physical implications are discussed. © 2007 Elsevier B.V. All rights reserved.

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ブラウン運動観測の学生実験について

青木健一郎， 柴崎彬

慶應義塾大学日吉紀要 31   21-52 2006年

研究論文（学術雑誌）, 単著

Energy transport in weakly anharmonic chains

Aoki K., Lukkarinen J., Spohn H.

Journal of Statistical Physics （Journal of Statistical Physics）  124 （ 124 ） 1105-1129 - 1129 2006年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00224715

　概要を見る

We investigate the energy transport in a one-dimensional lattice of oscillators with a harmonic nearest neighbor coupling and a harmonic plus quartic on-site potential. As numerically observed for particular coupling parameters before, and confirmed by our study, such chains satisfy Fourier's law: a chain of length N coupled to thermal reservoirs at both ends has an average steady state energy current proportional to 1/N. On the theoretical level we employ the Peierls transport equation for phonons and note that beyond a mere exchange of labels it admits nondegenerate phonon collisions. These collisions are responsible for a finite heat conductivity. The predictions of kinetic theory are compared with molecular dynamics simulations. In the range of weak anharmonicity, respectively low temperatures, reasonable agreement is observed. © Springer Science+Business Media, LLC 2006.

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On the construction of asymmetric orbifold models

Aoki K., D'Hoker E., Phong D.

Nuclear Physics B （Nuclear Physics B）  695 （ 1-2 ） 132 - 168 2004年09月

ISSN  05503213

　概要を見る

Various asymmetric orbifold models based on chiral shifts and chiral reflections are investigated. Special attention is devoted to the consistency of the models with two fundamental principles for asymmetric orbifolds: modular invariance and the existence of a proper Hilbert space formulation for states and operators. The interplay between these two principles is non-trivial. It is shown, for example, that their simultaneous requirement forces the order of a chiral reflection to be 4, instead of the naive 2. A careful explicit construction is given of the associated one-loop partition functions. At higher loops, the partition functions of asymmetric orbifolds are built from the chiral blocks of associated symmetric orbifolds, whose pairings are determined by degenerations to one-loop. © 2004 Elsevier B.V. All rights reserved.

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Time-reversible deterministic thermostats

青木 健一郎

Physica D: Nonlinear Phenomena （Physica D: Nonlinear Phenomena）  187 （ D187 ） 253-267 - 267 2004年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  01672789

　概要を見る

Seven different time-reversible deterministic thermostats are considered here and applied to a simple particle-based nonequilibrium heat-flow problem. This approach is robust. Results for all these different thermostats agree rather well for system widths of ten particle diameters or more. The simplest of the thermostats is the Gauss-Nosé-Hoover thermostat, based on kinetic-energy control. Higher moments of the particle momenta can be controlled by extensions of this idea involving as many as three additional thermostat variables. Generalizations of the deterministic thermostats suited to simulating "stochastic" and "Brownian" dynamics are discussed here too. © 2003 Elsevier B.V. All rights reserved.

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Spatial distributions of observables in systems under thermal gradients

青木 健一郎

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics （Physical Review E - Statistical, Nonlinear, and Soft Matter Physics）  E70 （ 5 1 ） 051203 2004年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  15393755

　概要を見る

The departure behavior of the observables from their thermal equilibrium expectation values was analyzed under heat flow in a steady-state nonequilibrium environment. The relationship between the momentum cumulants and the spatial distribution was also investigated. It was observed that the temperature profile for a given nonequilibrium steady state combined with deviations of physical observables could be used to develop a consistent description of spatial distribution of the observables. The results show that lower order cumulants characterize the difference of the nonequilibrium distribution from the one in local equilibrium.

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Two-loop superstrings on orbifold compactifications

青木 健一郎

Nuclear Physics B （Nuclear Physics B）  688 （ B688 ） 3-69 - 69 2004年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  05503213

　概要を見る

The two-loop chiral measure for superstring theories compactified on Z 2 reflection orbifolds is constructed from first principles for even spin structures. This is achieved by a careful implementation of the chiral splitting procedure in the twisted sectors and the identification of a subtle worldsheet supersymmetric and supermoduli dependent shift in the Prym period. The construction is generalized to compactifications which involve more general NS backgrounds preserving worldsheet supersymmetry. The measures are unambiguous and independent of the gauge slice. Two applications are presented, both to superstring compactifications where 4 dimensions are Z 2 -twisted and where the GSO projection involves a chiral summation over spin structures. The first is an orbifold by a single Z 2 -twist; here, orbifolding reproduces a supersymmetric theory and it is shown that its cosmological constant indeed vanishes. The second model is of the type proposed by Kachru-Kumar-Silverstein and additionally imposes a Z 2 -twist by the parity of worldsheet fermion number; it is shown here that the corresponding cosmological constant does not vanish pointwise on moduli space. © 2004 Elsevier B.V. All rights reserved.

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Lyapunov exponents and the extensivity of dimensional loss for systems in thermal gradients

Aoki K., Kusnezov D.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics （Physical Review E - Statistical, Nonlinear, and Soft Matter Physics）  68 （ 5 2 ） 562041 - 5620416 2003年11月

ISSN  1063651X

　概要を見る

An explicit relation between the dimensional loss (δ), entropy production, and transport under thermal gradients was discussed. It was found that the extensivity of δD in systems with bulk behavior followed from the relation. It was found that the maximum Lyapunov exponents in thermal equilibrium and δD in nonequilibrium depended on the choice of heat baths while their prodcuts was unique and macroscopic. The statistical errors in the numerical computation of δD were also elaborated.

Violations of local equilibrium and linear response in classical lattice systems

Aoki K., Kusnezov D.

Physics Letters, Section A: General, Atomic and Solid State Physics （Physics Letters, Section A: General, Atomic and Solid State Physics）  309 （ 5-6 ） 377 - 381 2003年03月

ISSN  03759601

　概要を見る

We quantitatively and systematically analyze how local equilibrium, and linear response in transport are violated as systems move far from equilibrium. This is done by studying heat flow in classical lattice models with and without bulk transport behavior, in 1-3 dimensions, at various temperatures. Equations of motion for the system are integrated numerically to construct the non-equilibrium steady states. Linear response and local equilibrium assumptions are seen to break down in a similar manner. We quantify the breakdown through the analysis of both microscopic and macroscopic observables and examine its transformation properties under general redefinitions of the non-equilibrium temperature. © 2003 Elsevier Science B.V. All rights reserved.

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Microscopic and Macroscopic Physics of Non-equilibrium Steady States Near and Far from Equilibrium

青木 健一郎

物性研究  （ 80 ） 139-144 2003年

研究論文（学術雑誌）, 共著

Lyapunov exponents, transport and the extensivity of dimensional loss in thermal gradients

青木 健一郎

Physics Review  （ E68 ） 056204-1---6 2003年

研究論文（学術雑誌）, 共著, 査読有り

文化系学生が学ぶ物理学実験

青木 健一郎

大学の物理教育  （ 11月 ） 32-35 2002年11月

研究論文（学術雑誌）, 単著, 査読有り

Nonequilibrium statistical mechanics of classical lattice ∅⁴ field theory

Aoki K., Kusnezov D.

Annals of Physics （Annals of Physics）  295 （ 1 ） 50 - 80 2002年01月

ISSN  00034916

　概要を見る

We study the nonequilibrium statistical mechanics of classical lattice 4 theory in thermal gradients of arbitrary strength. The steady-state physics of the theory in (1 + 1) dimensions is investigated from first principles and classified into dynamical regimes. The bulk properties associated with thermal transport are derived. Starting with thermal equilibrium, we examine the relation to the kinetic theory description of the behavior of the system. Green-Kubo transport coefficients are computed and compared to measured transport near and far from equilibrium, defining the scope of linear response and including an analysis of long-time tails. Local equilibrium is investigated and seen to explicitly break down under sufficiently strong gradients. Additional measures of the nonequilibrium steady state are also discussed as well as the connections to irreversible thermodynamics. © 2002 Elsevier Science (USA).

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Remarks on non-Hamiltonian statistical mechanics: Lyapunov exponents and phase-space dimensionality loss

青木 健一郎

Europhysics Letters （Europhysics Letters）  60 （ 60 ） 337-341 - 341 2002年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  02955075

　概要を見る

The dissipation associated with nonequilibrium flow processes is reflected by the formation of strange attractor distributions in phase space. The information dimension of these attractors is less than that of the equilibrium phase space, corresponding to the extreme rarity of nonequilibrium states. Here we take advantage of a simple model for heat conduction to demonstrate that the nonequilibrium dimensionality loss can definitely exceed the number of phase-space dimensions required to thermostat an otherwise Hamiltonian system.

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Non-Equilibrium Statistical Mechanics of Classical Lattice $phi^4$ Field Theory

青木 健一郎

Annals of Physics  （ 295 ） 50-80 2002年

研究論文（学術雑誌）, 共著, 査読有り

Violations of local equilibrium and linear response in classical lattice theories

青木 健一郎

素粒子論研究  （ 101 ） A98---A104 2002年

研究論文（学術雑誌）, 共著

Fermi-Pasta-Ulam β model: Boundary jumps, fourier's law, and scaling

Aoki K., Kusnezov D.

Physical Review Letters （Physical Review Letters）  86 （ 18 ） 4029 - 4032 2001年04月

ISSN  00319007

　概要を見る

The temperature and size dependence of the thermal conductivity in the Fermi-Pasta-Ulam β model were computed. A quantitative understanding of these effects was obtained. Further, dynamical regimes were defined based on the interplay of surface and volume effects.

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FPU $beta$ model: Boundary Jumps, Fourier's Law and Scaling

青木 健一郎

Physics Review Letters  （ 86 ） 4029---4032 2001年

研究論文（学術雑誌）, 共著, 査読有り

Meson mass differences in two dimensional gauged four-Fermi models

青木 健一郎

Physical Review D （Physical Review D）  65 （ D65 ） 025003-1---11 2001年

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  05562821

　概要を見る

We quantitatively analyze the meson mass inequality relations of two dimensional gauged four-Fermi models in the large N limit. The class of models we study includes the 't Hooft model and the chiral and nonchiral Gross-Neveu models as special points in the space of field theories. Cases in which the chiral symmetry is spontaneously or explicitly broken are both studied. We study the meson mass differences quantitatively and define a susceptibility which allows us to systematically analyze these quantities. In the generalized Gross-Neveu model limit, we derive an analytic expression for this susceptibility. Even though no analytic proof of the validity of the classic mass inequality exists for the generic case, the mass difference is found to have the standard sign throughout most of the parameter space. We point out that the difference might have the opposite sign in certain cases. © 2001 The American Physical Society.

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Non-equilibrium steady states and transport in the classical lattice φ⁴ theory

Aoki K., Kusnezov D.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics （Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics）  477 （ 1-3 ） 348 - 354 2000年03月

ISSN  03702693

　概要を見る

We study the classical non-equilibrium statistical mechanics of scalar field theory on the lattice. Steady states are analyzed near and far from equilibrium. The bulk thermal conductivity is computed, including its temperature dependence. We examine the validity of linear response predictions, as well as properties of the non-equilibrium steady state. We find that the linear response theory applies to visibly curved temperature profiles as long as the thermal gradients are not too strong. We also examine the transition from local equilibrium to local non-equilibrium. (C) 2000 Elsevier Science B.V.

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Bulk properties of anharmonic chains in strong thermal gradients: Non-equilibrium φ4 theory

Aoki K., Kusnezov D.

Physics Letters, Section A: General, Atomic and Solid State Physics （Physics Letters, Section A: General, Atomic and Solid State Physics）  265 （ 4 ） 250 - 256 2000年01月

ISSN  03759601

　概要を見る

We study nonequilibrium properties of a one-dimensional lattice Hamiltonian with quartic interactions in strong thermal gradients. Nonequilibrium temperature profiles, T(x), are found to develop significant curvature and boundary jumps. From the determination of the bulk thermal conductivity, we develop a quantitative description of T(x) including the jumps. (C) 2000 Published by Elsevier Science B.V.

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Classical $phi^4$ Lattice Field Theory in Strong Thermal Gradients

青木 健一郎

素粒子論研究  （ 100 ） E56-E59 2000年

研究論文（学術雑誌）, 共著

Bulk properties of anharmonic chains in strong thermal gradients: non-equilibrium $phi^4$ theory

青木 健一郎

Physics Letters  （ A265 ） 250-256 2000年

研究論文（学術雑誌）, 共著, 査読有り

Non-Equilibrium Steady States and Transport in $phi ^4$ Theory

青木 健一郎

Physics Letters  （ B477 ） 348-354 2000年

研究論文（学術雑誌）, 共著, 査読有り

Physics of the gauged four fermi model in $(1+1)$ dimensions

青木 健一郎

Physical Review  （ D60 ） 096004--1---13 1999年

研究論文（学術雑誌）, 共著, 査読有り

Non-decoupling effects due to a dimensionful coupling

Aoki K.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics （Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics）  418 （ 1-2 ） 125 - 133 1998年01月

ISSN  03702693

　概要を見る

We show that the dimensionful scalar cubic coupling in 3 + 1 dimensions gives rise to non-decoupling effects and analyze the behavior of these effects. In the process, we clarify how it is perturbatively consistent to construct theories in which the cubic coupling is dominant. We use the scalar sector of the Supersymmetric Standard Model as an example. We discuss how the non-decoupling effects may be analyzed systematically. © 1998 Elsevier Science B.V.

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Non-critical strings at high energy

Aoki K., D'Hoker E.

Nuclear Physics B （Nuclear Physics B）  490 （ 1-2 ） 40 - 74 1997年04月

ISSN  05503213

　概要を見る

We consider scattering amplitudes in non-critical string theory of N external states in the limit where the energy of all external states is large compared to the string tension. We argue that the amplitudes are naturally complex analytic in the matter central charge c and we propose to define the amplitudes for arbitrary value of c by analytic continuation. We show that the high energy limit is dominated by a saddle point that can be mapped onto an equilibrium electrostatic energy configuration of an assembly of N pointlike (Minkowskian) charges, together with a density of charges arising from the Liouville field. We argue that the Liouville charges accumulate on segments of curves, and produce quadratic branch cuts on the world-sheet. The electrostatics problem is solved for string tree level in terms of hyper-elliptic integrals and is given explicitly for three-and four-point functions. We show that the high energy limit should behave in a string-like fashion with exponential dependence on the energy scale for generic values of c. © 1997 Elsevier Science B.V.

High energy scattering of non-critical strings

Aoki K., D'Hoker E.

International Journal of Modern Physics A （International Journal of Modern Physics A）  12 （ 6 ） 1253 - 1263 1997年03月

ISSN  0217751X

　概要を見る

We summarize recent work, in which we consider scattering amplitudes of non-critical strings in the limit where the energy of all external states is large compared to the string tension. We show that the high energy limit is dominated by a saddle point that can be mapped onto an electrostatic equilibrium configuration of an assembly of charges associated with the external states, together with a density of charges arising from the Liouville field. The Liouville charges accumulate on line segments, which produce quadratic branch cuts on the worldsheet. The electrostatics problem is solved for string tree level in terms of hyperelliptic integrals and is given explicitly for the 3- and 4-point functions. For generic values of the central charge, the high energy limit behaves in a string-like fashion, with exponential energy dependence. © World Scientific Publishing Company.

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(1+1)-dimensional QCD with fundamental bosons and fermions

Aoki K., Ichihara T.

Physical Review D （Physical Review D）  52 （ 11 ） 6435 - 6444 1995年

ISSN  05562821

　概要を見る

We analyze the properties of mesons in (1+1)-dimensional QCD with bosonic and fermionic ''quarks'' in the large Nc limit. We study the spectrum in detail and show that it is impossible to obtain massless mesons including boson constituents in this model. We quantitatively show how the QCD mass inequality is realized in two-dimensional QCD. We find that the mass inequality is close to being an equality even when the quarks are light. Methods for obtaining the properties of ''mesons'' formed from boson and/or fermion constituents are formulated in an explicit manner convenient for further study. We also analyze how the physical properties of the mesons such as confinement and asymptotic freedom are realized. © 1995 The American Physical Society.

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Triviality, perturbation theory and Z → bb

Aoki K., Peris S.

Physics Letters B （Physics Letters B）  335 （ 3-4 ） 470 - 478 1994年09月

ISSN  03702693

　概要を見る

We compute the large-mt contributions to the Zbb vertex in the Standard Model non-perturbatively using both the 1/Nc and the 1/NF expansions. Triviality and its consequences for the perturbative result are systematically analyzed. In particular, we point out that the effect of triviality is already important at the two-loop level for a heavy Higgs (600 GeV < MH < 1 TeV) even when the top mass is below 200 GeV. © 1994.

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Non-decoupling, triviality and the ρ{variant} parameter

Aoki K., Peris S.

Zeitschrift für Physik C Particles and Fields （Zeitschrift für Physik C Particles and Fields）  61 （ 2 ） 303 - 312 1994年06月

ISSN  01709739

　概要を見る

The dependence of the ρ{variant} parameter on the mass of the Higgs scalar and the top quark is computed non-perturbatively using the 1/NF expansion in the standard model. We find an explicit expression for the ρ{variant} parameter that requires the presence of a physical cutoff. This should come as no surprise since the theory is presumably trivial. By taking this cutoff into account, we find that the ρ{variant} parameter can take values only within a limited range and has finite ambiguities that are suppressed by inverse powers of the cutoff scale, the so called "scaling-violations". We find that large deviations from the perturbative results are possible, but only when the cutoff effects are also large. © 1994 Springer-Verlag.

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Boson-fermion bound states in two-dimensional QCD

Aoki K.

Physical Review D （Physical Review D）  49 （ 1 ） 573 - 574 1994年

ISSN  05562821

　概要を見る

We derive the boson-fermion bound state equation in a two-dimensional gauge theory in the large-Nc limit. We analyze the properties of this equation and, in particular, find that the mass trajectory is linear with respect to the bound state level for the higher mass states. © 1994 The American Physical Society.

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Large-order behavior of nondecoupling effects in the standard model and triviality

Aoki K.

Physical Review D （Physical Review D）  49 （ 3 ）  1994年

ISSN  05562821

　概要を見る

We compute some nondecoupling effects in the standard model, such as the ρ parameter, to all orders in the coupling constant expansion. We analyze their large order behavior and explicitly show how they are related to the nonperturbative cutoff dependence of these nondecoupling effects due to the triviality of the theory. © 1994 The American Physical Society.

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Nonperturbative evidence for nondecoupling of heavy fermions

Aoki K., Peris S.

Physical Review Letters （Physical Review Letters）  70 （ 12 ） 1743 - 1746 1993年

ISSN  00319007

　概要を見る

We investigate, using a 1/N expansion, the behavior of a parameter in the scalar-fermion sector of the standard model that shows perturbative nondecoupling as the fermion becomes heavy. This low-energy parameter is related to the S parameter defined through W3-B mixing. We obtain the leading 1/N contribution to this parameter that, if expanded perturbatively, collapses to its constant one-loop result. Nonperturbatively, we find that as the mass of the fermion approaches the triviality scale the behavior of the parameter is nonuniversal and shows nondecoupling. © 1993 The American Physical Society.

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W-gravity and generalized Lax equations for (super) Toda theory

Aoki K., D'Hoker E.

Nuclear Physics, Section B （Nuclear Physics, Section B）  387 （ 3 ） 576 - 586 1992年12月

ISSN  05503213

　概要を見る

We generalize the Lax pair and Bäcklund transformations for Toda and N = 1 super Toda equations to the case of arbitrary world-sheet background geometry. We use the fact that the Toda equations express constant curvature conditions, which arise naturally from flatness conditions equivalent to the W-gravity equation of motion. © 1992.

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Large-NF solution of the quark-Higgs sector of the supersymmetric standard model

Aoki K.

Physical Review D （Physical Review D）  46 （ 3 ） 1123 - 1130 1992年

ISSN  05562821

　概要を見る

We solve a model of a Higgs supermultiplet coupled to a quark (or a lepton) supermultiplet in the large-NF limit including the effects of soft supersymmetry-breaking terms. We find that the model needs to be defined with a cutoff and we obtian the spectrum of the model in the region where the masses of the particles remain below the cutoff scale of the model. The model corresponds to the quark-Higgs (or lepton-Higgs) sector of the supersymmetric versions of the standard model when the quantum corrections due to only the Yukawa-Higgs couplings are considered. © 1992 The American Physical Society.

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Effects of fermion back reaction on instantons

Aoki K., Mazur P.

Nuclear Physics, Section B （Nuclear Physics, Section B）  352 （ 2 ） 507 - 527 1991年03月

ISSN  05503213

　概要を見る

We show how systematically incorporate back reaction into fermion number violating amplitudes in Yang-Mills theories. We discuss the possible recovery of unittarity at high energies for these processes. © 1991.

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Large-NF expansion for the Yukawa coupling

Aoki K.

Physical Review D （Physical Review D）  44 （ 5 ） 1547 - 1554 1991年

ISSN  05562821

　概要を見る

By enlarging the number of fermion species and sclar fields, we generalize the Yukawa-Higgs sector of the standard model. We solve this model to leading order in a 1NF expansion. We study the behavior of the fermion mass and the width when they are below the cutoff scale of the theory. Other Yukawa-Higgs models with different chiral structures are also studied. We find that the mass of the fermion is finite and is below the cutoff scale for any finite on-shell Yukawa coupling in the chiral models. © 1991 The American Physical Society.

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Unitarity of closed superstring perturbation theory

Aoki K., D'Hoker E., Phong D.

Nuclear Physics, Section B （Nuclear Physics, Section B）  342 （ 1 ） 149 - 230 1990年09月

ISSN  05503213

　概要を見る

The scattering amplitudes for the covariant formulation of closed Type II and heterotic superstrings are shown to be equivalent, order-by-order in string perturbation theory, to those of the light-cone interacting string picture. This establishes the unitarity of covariant superstring perturbation theory and the Lorentz invariance of the light-cone superstring. © 1990.

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Topological supergravity in two dimensions

Montano D., Aoki K., Sonnenschein J.

Physics Letters B （Physics Letters B）  247 （ 1 ） 64 - 70 1990年09月

ISSN  03702693

　概要を見る

The topological theory of OSp(2|1;R) flat gauge connections is shown to be equivalent to two-dimensional supergravity. By choosing a particular gauge fixing of the SL(2;R) (OSp(2|1;R) invariance we make contact with the Liouville theory approach to two-dimensional gravity (supergravity). We discuss the scaling and multriritical behavior of two-dimensional supergravity. © 1990.

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Correlation of Z<inf>N</inf> super twist fields on the sphere

Aoki K.

Nuclear Physics, Section B （Nuclear Physics, Section B）  326 （ 2 ） 393 - 410 1989年11月

ISSN  05503213

　概要を見る

The correlation function of the ZN super twist fields is calculated on the sphere. Also, the degeneration behavior of the higher genus partition function is used to derive the spectrum of dimensions for the non-abelian super twist fields. © 1989.

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Twisted non-Abelian determinants on Riemann supersurfaces

Aoki K., Periwal V.

Communications in Mathematical Physics （Communications in Mathematical Physics）  124 （ 2 ） 301 - 306 1989年06月

ISSN  00103616

　概要を見る

We calculate the twisted supersymmetric determinants that are necessary for the study of the propagation of spinning strings on arbitrary orbifolds. We calculate the degeneration behaviour of multiloop amplitudes for twisted internal sectors. We use this to derive the spectrum of dimensions of twist fields. © 1989 Springer-Verlag.

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Heat kernels and super determinants of Laplace operators on super Riemann surfaces

Aoki K.

Communications in Mathematical Physics （Communications in Mathematical Physics）  117 （ 3 ） 405 - 429 1988年09月

ISSN  00103616

　概要を見る

Heat kernels of Laplacians on superfields of arbitrary tensor weight on super Riemann surfaces are constructed, and are used to compute the super determinants of these operators in terms of the Selberg super zeta function. © 1988 Springer-Verlag.

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