arXiv subjects

Koshiro Suzuki

Publications and source records attributed to Koshiro Suzuki.

14 recordsLinked to original sources

arXiv2019

Theory for the rheology of dense non-Brownian suspensions: divergence of viscosities and $μ$-$J$ rheology

A systematic microscopic theory for the rheology of dense non-Brownian suspensions characterized by the volume fraction $φ$ is developed. The theory successfully derives the critical behavior in the vicinity of the jamming point (volume fraction $φ_{J}$), for both the pressure $P$ and the shear stress $σ_{xy}$, i.e. $P \sim σ_{xy} \sim \dotγη_0 δφ^{-2}$, where $\dotγ$ is the shear rate, $η_0$ is the shear viscosity of the solvent, and $δφ= φ_J - φ> 0$ is the distance from the jamming point. It also successfully describes the behavior of the stress ratio $μ= σ_{xy}/P$ with respect to the viscous number $J=\dotγη_{0}/P$.

cond-mat.soft↗

arXiv2015

Divergence of Viscosity in Jammed Granular Materials: A Theoretical Approach

A theory for jammed granular materials is developed with the aid of a nonequilibrium steady-state distribution function. The approximate nonequilibrium steady-state distribution function is explicitly given in the weak dissipation regime by means of the relaxation time. The theory quantitatively agrees with the results of the molecular dynamics simulation on the critical behavior of the viscosity below the jamming point without introducing any fitting parameter.

cond-mat.soft↗

arXiv2014

Rheology of Dense Sheared Granular Liquids

The rheology of dense sheared granular liquids is investigated based on the mode-coupling theory (MCT). This extended MCT includes correlations for the density-current mode as well as the density-density correlation mode, and a self-consistent coupling equation for the energy balance condition. The extended MCT exhibits disappearance of the two-step relaxation of the density-density correlation function, and also successfully reproduces the density dependence of the shear viscosity for volume fractions between 0.50 and 0.60, if we shift the density. However, it predicts unphysical tendency for the granular temperature. The cause of this drawback and the possibilities of its amendment are discussed.

cond-mat.stat-mech↗

arXiv2014

Fractional Einstein relation for strongly disordered semiconductors

A novel Einstein relation (fractional Einstein relation, FER) for the electric conduction in non-crystalline semiconductors is presented. FER and the generalized Einstein relation (GER) [Phys. Rev. E 8, 1296 (1998)] are compared to the result of the Monte Carlo (MC) simulation, and is confirmed that FER exhibits better agreement than GER. The cruial feature of FER is that it reflects the violation of the detailed balance in the coarse-grained hopping process, while it is preserved in the original Einstein relation or GER.

cond-mat.dis-nn↗

arXiv2013

DC electric field effect on the anomalous exponent of the hopping conduction in the one-dimensional disorder model

DC electric field effect on the anomalous exponent of the hopping conduction in the disorder model is investigated. First, we explain the model and derive an analytical expression of the effective waiting time for the general case. We show that the exponent depends on the external field. Then we focus on a one-dimensional system in order to illustrate the features of the anomalous exponent. We derive approximate expressions of the anomalous exponent of the system analytically. For the case of a weak field, the anomalous exponent is consistent with that of diffusive systems. This is consistent with the treatments of Barkai et al. [Phys. Rev. E {\bf 63}, 046118 (2001)] and our result supports their theory. On the other hand, for the case of a strong field and a strong disorder, the time evolution of the exponent clearly differs from that in the weak field. The exponent is consistent with the well-known expression of the anomalous exponent in the Multiple Trapping Model at mesoscopic time scales. In the long time limit, a transition of the anomalous exponent to the same value of the weak field occurs. For the case of a strong field and a weak disorder, the exponent is equal to 1 and thus the diffusion is normal. These findings are verified by the Monte Carlo simulation.

cond-mat.dis-nn↗

arXiv2013

Nonequilibrium mode-coupling theory for uniformly sheared underdamped systems

Mode-coupling theory for uniformly sheared underdamped systems with an isothermal condition is presented. As a result of the isothermal condition, it is shown that the shear stress exhibits significant relaxation at the alpha-relaxation regime due to the cooling effect which is accompanied by the growth of the current fluctuation. This indicates that nonequilibrium underdamped MCT is not equivalent to the corresponding overdamped MCT, even at long time-scales after the early stage of the beta relaxation. It is verified that the effect of correlations to the density-current modes is, however, negligible in sheared thermostated underdamped systems.

cond-mat.stat-mech↗

arXiv2013

Mode coupling theory for sheared granular liquids

Sheared granular liquids are studied by the mode coupling theory. It is shown that, in contrast to thermostatted systems, current correlations play an essential role in the dynamics. The theory predicts that the plateau of the density time-correlator disappears for most situations, while it appears in the elastic limit. The result is compatible with molecular dynamics simulations.

cond-mat.stat-mech↗

arXiv2012

Nonequilibrium mode-coupling theory for uniformly sheared underdamped systems

Nonequilibrium mode-coupling theory (MCT) for uniformly sheared underdamped systems is developed, starting from the microscopic thermostatted SLLOD equation, and the corresponding Liouville equation. Special attention is paid to the translational invariance in the sheared frame, which requires an appropriate definition of the transient time-correlators. The derived MCT equation satisfies the alignment of the wavevectors, and is manifestly translationally invariant. Isothermal condition is implemented by the introduction of the current fluctuation in the dissipative coupling to the thermostat. This current fluctation grows in the $α$-relaxation regime, which generates a deviation of the yield stress in the glassy phase from the overdamped case. Response to a perturbation of the shear rate demonstrates an inertia effect which is not observed in the overdamped case. Our theory turns out to be a non-trivial extension of the theory by Fuchs and Cates (J. Rheol. 53(4), 2009) to underdamped systems. Since our starting point is identical to that by Chong and Kim (Phys. Rev. E 79, 2009), the contradictions between Fuchs-Cates and Chong-Kim are resolved.

cond-mat.stat-mech↗

arXiv2012

Space-time dependence of the anomalous exponent of electric transport in the disorder model

Space-time dependence of the anomalous exponent of electric transport in the disorder model is presented. We show that the anomalous exponent depends on time, according to the time-evolution of the number of the effective neighbouring sites. Transition from subdiffusive to normal transport at long-enough time is recovered. The above result indicates that the spatial structure, specifically the network structure, of the hopping sites might be a novel element which determines the anomalous exponent. This leads to the feature that the scaling property of the electric transport to time is insensitive to other elements, such as the distance of the sites or the spatial dimension of the system. These findings are verified by means of Monte Carlo simulation. The relation of the result to the conventional knowledge of the Multiple Trapping Model is shown by deriving it as a special case of the disorder model.

cond-mat.dis-nn↗

arXiv2002

Investigation of noscale supersymmetry breaking models with a gauged U(1)_{B-L} symmetry

Noscale supersymmetry (SUSY) breaking model is investigated in the minimal extension of the minimal supersymmetric standard model (MSSM) with a gauged U(1)_{B-L} symmetry. We specifically consider a unification-inspired model with the gauge groups SU(3)_{C} \times SU(2)_{L} \times U(1)_Y \times U(1)_{B-L} \subset SU(5) \times U(1)_{5} for illustration. While the noscale boundary condition at the grand unification scale (M_{G}\simeq 2\times 10^{16} GeV) in the MSSM is not consistent with phenomenological constraints, we show that it is if the gaugino of the U(1)_{5} multiplet is several times heavier than the gauginos of the MSSM. However, if SU(5) \times U(1)_{5} is further embedded in a larger simple group, e.g. SO(10), the noscale boundary condition at M_{G} is inconsistent with phenomenological constraints. If we relax the noscale boundary condition and allow non-zero soft scalar masses for the Higgs fields which spontaneously break the U(1)_{5} symmetry, the resultant spectrum of SUSY particles becomes consistent with all the phenomenological constraints, even if we impose the GUT relation on the gauge coupling and the gaugino mass of the U(1)_{5}. In this case, the SUSY CP problem is also solved, since the condition Bμ=0 at the boundary can be imposed consistently with the electroweak symmetry breaking.

hep-ph↗

arXiv2001

Gauge Mediation Models with Neutralino Dark Matter

We study gauge mediation models of supersymmetry breaking with neutralino LSP. These models are naturally realized by embedding the usual four-dimensional gauge mediation models into a higher-dimensional spacetime such as $M^4 \times S^1 / Z_{2}$. We calculate the relic abundance of the neutralino LSP in these models and show that there exist wide parameter regions where the neutralino LSP constitutes the dominant component of the cold dark matter. These regions evade constraints from collider experiments such as Higgs mass bounds and $b \ra s γ$, and also provide the value for the muon anomalous magnetic moment which is consistent with the SUSY explanation of the deviation from the standard model prediction.

hep-ph↗

arXiv2001

Constraints on Inflation Models from Supersymmetry Breakings

Effects of soft SUSY-breaking terms on inflation potentials are discussed. There exist generic constraints that must be satisfied in order not for the inflaton potential to loose its flatness. We examine explicitly the constraints in the case of a hybrid inflation model and find that the coupling constant λbetween the inflaton and the ``water-fall-direction'' field is bounded as 2.0 \times 10^{-6} < λ. This is a highly non-trivial result. Indeed, if we adopt the severest constraint from avoiding the problem of the gravitinos produced non-thermally, λ< 7.4 \times 10^{-6} is required, under a reasonable assumption on the reheating process. This means that the hybrid inflation model marginally has a viable parameter space. We also discuss analogous constraints on other inflation models.

hep-ph↗

arXiv2000

Cosmological Gravitino Problem in Gauge-Mediated Supersymmetry Breaking Models

We investigate the cosmological gravitino problem in gauge-mediated supersymmetry breaking models, where the gravitino becomes in general the lightest supersymmetric particle (LSP). In order to avoid the overclosure of the stable gravitino, the reheating temperature of inflation $T_R$ should be low enough. Furthermore, if the gravitino mass is larger than about 100 MeV, the decay of the next-to-LSP (NLSP) into the gravitino may modify disastrously the abundances of the light elements predicted by the big-bang nucleosynthesis (BBN). We consider the case in which the lighter stau is the NLSP and derive cosmological constraints from the BBN on the stau NLSP decay. We obtain a lower bound on the mass of stau $m_{\staul}$, which is more stringent than the current experimental limit $m_{\staul} > 90$ GeV for the gravitino mass region $m_{3/2} \gsim 5$ GeV. This lower bound, together with the overclosure constraint on the stable gravitino, gives an upper bound on $T_{R}$. We find that the reheating temperature can be as high as $10^9$--$10^{10}$ GeV for $m_{3/2} \simeq 5$--100 GeV.

hep-ph↗

arXiv1999

A Relation on Gaugino Masses in a Supersymmetric SO(10)_GUT x SO(6)_H Unified Model

The doublet-triplet splitting problem in supersymmetric grand unified theories is elegantly solved in a supersymmetric SO(10)_GUT x SO(6)_H model. In this model, the gauginos in the supersymmetric standard model do not respect the usual GUT gaugino mass relation. We point out that in spite of non-unified gaugino masses there is one nontrivial relation among gaugino masses in the model. Thus, it can be used to test the model in future experiments.

hep-ph↗