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井上 悠平*; 野々山 朋信*; Kang, Z.; 藪中 俊介; 津川 暁
Journal of the Physical Society of Japan, 94(9), p.094001_1 - 094001_6, 2025/09
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)Particles that self-propel owing to changes in their own internal state are called self-propelled particles and are driven by the Marangoni effect caused by concentration and/or temperature gradients. As the propulsion speed increases, they become elliptically shaped. However, the driving forces behind this phenomenon are still not completely understood. Therefore, we used a numerical method to confirm whether elliptical deformation actually occurred in the self-propulsion of a droplet, and quantitatively confirmed how the surface tension of the droplet changed. As a result, we confirmed that the second mode of the surface tension was the driving force of the contour of the droplet. Furthermore, the competing combination of the fluid pressure gradient and Korteweg force associated with the reacting molecules was the actual driving force of the fluid that induced a self-organized flow.
藪中 俊介
Physics of Fluids, 37(8), p.083102_1 - 083102_8, 2025/08
被引用回数：1 パーセンタイル：47.35(Mechanics)We calculate the drag coefficient of a spherical particle suspended in a near-critical binary fluid mixture. To capture the scaling behavior associated with critical adsorption in the strong adsorption regime, we employ the framework of local renormalized functional theory. Previous theoretical studies encountered numerical difficulties when attempting to solve the coupled hydrodynamic and chemical potential equations, expressed as integral equations, for systems with large bulk correlation lengths. These difficulties limited direct comparison with experimental results. In this study, we overcome those limitations by reformulating the hydrodynamic equations as a set of ordinary differential equations using a compactified radial coordinate. This approach enables more stable numerical computation and facilitates the implementation of appropriate boundary conditions at large distances from the particle. As a result, we successfully compute the drag coefficient over a broader range of bulk correlation lengths than in previous works and compare our theoretical predictions with available experimental data.
藪中 俊介; Delamotte, B.*
Journal of Statistical Mechanics; Theory and Experiment, 2025, p.023204_1 - 023204_22, 2025/02
We revisit the critical behavior of classical frustrated systems using the nonperturbative renormalization group (NPRG) equation. Our study is performed within the local potential approximation of this equation to which is added the flow of the field renormalization. Our flow equations are functional to avoid possible artifacts coming from the field expansion of the fixed point potential which consists in keeping only a limited number of coupling constants. We explain in detail our numerical implementation, its advantages and the difficulties encountered in the vicinity of 
. For N-component spins, the function 
separating the regions of first and second order transitions in the 
plane is computed for d between 4 and 2.3. Our results confirm what was previously found with cruder approximations of the NPRG equation and contradict both the fixed dimension perturbative approach and some of the results obtained within the conformal bootstrap approach.
藪中 俊介; 藤谷 洋平*
Physical Review E, 109(6), p.064610_1 - 064610_19, 2024/06
被引用回数：5 パーセンタイル：73.54(Physics, Fluids & Plasmas)We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point, and study its transport through a capillary tube linking two large reservoirs. We assume that short-range interactions cause preferential adsorption of one component onto the tube's wall. For transport processes induced by gradients of the pressure, composition, and temperature along a cylindrical tube, we obtain the formulas of the Onsager coefficients to extend our previous results on isothermal transport, assuming the critical composition in the middle of each reservoir in the reference equilibrium state.
) models at large 藪中 俊介; Delamotte, B.*
Physical Review Letters, 130(26), p.261602_1 - 261602_6, 2023/06
被引用回数：1 パーセンタイル：15.13(Physics, Multidisciplinary)We show that at 
and below its upper critical dimension, 
, the critical and tetracritical behaviors of the O
models are associated with the same renormalization group fixed point (FP) potential. Only their derivatives make them different with the subtleties that taking their 
limit and deriving them do not commute and that two relevant eigenperturbations show singularities. This invalidates both the 
- and the 
- expansions. We also show how the Bardeen-Moshe-Bander line of tetracritical FPs at and 
can be understood from a finite- analysis.
analysis of the 
models; Nonperturbative cuspy fixed points and their nontrivial homotopy at finite 藪中 俊介; Fleming, C.*; Delamotte, B.*
Physical Review E, 106(5), p.054105_1 - 054105_29, 2022/11
被引用回数：6 パーセンタイル：55.79(Physics, Fluids & Plasmas)We summarize the usual implementations of the large- limit of models and show in detail why and how they can miss some physically important fixed points when they become singular in the infinite . Using Wilson's renormalization group in its functional nonperturbative versions, we show how the singularities build up as increases. In the Wilson-Polchinski version of the nonperturbative renormalization group, we show that the singularities are cusps, which become boundary layers for finite but large values of . The corresponding fixed points being never close to the Gaussian, are out of reach of the usual perturbative approaches. We find four new fixed points and study them in all dimensions and for all and show that they play an important role for the tricritical physics of models. Finally, we show that some of these fixed points are bi-valued when they are considered as functions of 
and thus revealing important and nontrivial homotopy structures.
黒山 和幸*; 松尾 貞茂*; 村本 丈*; 藪中 俊介; Velentin, S. R.*; Ludwig, A.*; Wieck, A. D.*; 都倉 康弘*; 樽茶 清悟*
Physical Review Letters, 129(9), p.095901_1 - 095901_6, 2022/08
被引用回数：4 パーセンタイル：39.48(Physics, Multidisciplinary)We report on experimental observations of charge-spin cooperative dynamics of two-electron states in a GaAs double quantum dot located in a nonequilibrium phonon environment. When the phonon energy exceeds the lowest excitation energy in the quantum dot, the spin-flip rate of a single electron strongly enhances. In addition, originated from the spatial gradient of phonon density between the dots, the parallel spin states become more probable than the antiparallel ones. These results indicate that spin is essential for further demonstrations of single-electron thermodynamic systems driven by phonons, which will greatly contribute to understanding of the fundamental physics of thermoelectric devices.
藪中 俊介; 藤谷 洋平*
Physics of Fluids, 34(5), p.052012_1 - 052012_18, 2022/05
被引用回数：7 パーセンタイル：51.19(Mechanics)弱い圧力、化学ポテンシャル勾配を加えた場合の毛細管中での二元混合系の等温環境下の輸送を考える。壁面での選択的吸着効果が強い際には、壁面近くに相関長程度の厚さの吸着層が形成される。そのため毛細管中の組成が不均一となり、相関長も不均一となる。我々はこのような状況での流体力学をLocal renormalized functional theoryを用いて考察し流量の計算を行った。
藪中 俊介
no journal, ,
We revisit the critical behavior of classical frustrated systems using the nonperturbative renormalization group (NPRG) equation. Our study is performed within the local potential approximation of this equation to which is added the flow of the field renormalization. Our flow equations are functional to avoid possible artifacts coming from field expansions which consists in keeping only a limited number of coupling constants. The function separating the regions of first and second order in the plane is computed for between 4 and 2.5. Our results are compared with both the fixed dimension perturbative approach and the results obtained within the conformal bootstrap approach.
藪中 俊介
no journal, ,
若手奨励賞「ソフトマター、アクティブマターにおける相転移、分岐現象の連続体理論による研究」の内容、(1)選択的溶媒和効果を持つイオンで構成された電気二重層に関する新しい表面相転移、(2)臨界点近くの2元混合系中のコロイドの抵抗係数の計算の研究を講演する。
藪中 俊介; Delamotte, B.*
no journal, ,
We find that the multicritical fixed point structure of the O() models is much more complicated than widely believed. In particular, we find new nonperturbative fixed points in three dimensions (
) as well as at 
and for 
. These fixed points come together with an intricate homotopy structure when they are considered as functions of and 
. The fact that the new nonperturbative fixed points at had not been found questions the conventional large expansion, which plays a fundamental role in quantum and statistical field theory. We show on the example of the O model that at , its standard implementation misses in all dimensions below 
the new nonperturbative fixed points. These new fixed points show singularities under the form of cusps at in their effective potential that become a boundary layer at finite . We show that they have a physical impact on the multicritical physics of the 
) model at finite . We also show that the boundary layer also plays a role for the tetracritical case 
, but in a different way than the tricritical case.
model at and 藪中 俊介
no journal, ,
We study the Bardeen-Moshe-Bander lines in O (N) model at in and 8/3. The first line in consists of the tricritical fixed points and ends at the Bardeen-Moshe-Bander fixed point. The large limit that allows us to find the BMB line must be taken on particular trajectories in the (d, N) plane: 
and not at fixed dimension . Our study also reveals that the known BMB line is only half of the true line of fixed points, the second half being made of singular fixed points. We also discuss how the critical exponent 
becomes 3 and scale invariance is broken at the BMB FP at and .
藪中 俊介; 藤谷 洋平*
no journal, ,
弱い圧力,化学ポテンシャル勾配を加えた場合の毛細管中での二元混合系の浸透現象を考える。壁面での選択的吸着効果が強い際には、壁面近くに相関長程度の厚さの吸着層が形成される。そのため毛細管中の組成が不均一となり、相関長も不均一となる。我々はこのような状況での流体力学をLocal renormalized functional theoryを用いて考察し流量の計算を行ってきた。今回の講演では、流量の換算温度に関するスケーリング則に関して議論する。
藪中 俊介; Fleming, C.*; Delamotte, B.*
no journal, ,
We summarize the usual implementations of the large N limit of O(N) models and show in detail why and how they can miss some physically important fixed points when they become singular in the infinite N. Using Wilson's renormalization group in its functional nonperturbative versions, we show how the singularities build up as N increases. In the Wilson-Polchinski version of the nonperturbative renormalization group, we show that the singularities are cusps, which become boundary layers for finite but large values of N. The corresponding fixed points being never close to the Gaussian, are out of reach of the usual perturbative approaches. We find four new fixed points and study them in all dimensions and for all N and show that they play an important role for the tricritical physics of O(N) models. Finally, we show that some of these fixed points are bi-valued when they are considered as functions of d and N thus revealing important and nontrivial homotopy structures.
藪中 俊介; 藤谷 洋平*
no journal, ,
We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point, to consider its dynamics through a capillary tube. We assume preferential adsorption of one component on the tube's wall due to short-range interactions. The resultant adsorption layer becomes very thick near the critical point, inside which the thermal force density under a temperature gradient is nonvanishing. This enables a temperature difference to cause the total mass flow of the mixture, which represents thermoosmosis. We predict that, for any binary mixture near the critical point with the upper (lower) critical solution temperature, the direction of the total mass flow is the same as (opposite to) the temperature gradient, respectively.
藪中 俊介
no journal, ,
We study the Bardeen-Moshe-Bander lines in O (N) model at in and 8/3. The first line in consists of the tricritical fixed points and ends at the Bardeen-Moshe-Bander fixed point. The large limit that allows us to find the BMB line must be taken on particular trajectories in the (d, N) plane: and not at fixed dimension 
. Our study also reveals that the known BMB line is only half of the true line of fixed points, the second half being made of singular fixed points. The potentials of these singular fixed points show a cusp for a finite value of the field and their finite N counterparts a boundary layer. The second line in 
consists of the tricritical fixed points and ends at the Wison-Fisher fixed point. This seems paradoxical since the stabilities of the Wilson-Fisher fixed point and the tertactical fixed point are different. We show that only their derivatives of the potentials make them different with the subtleties that taking their limit and deriving them do not commute and that two relevant eigenperturbations show singularities at . We also discuss the finite-N realization of the second line of FPs in .
藪中 俊介
no journal, ,
本講演では臨界点に近い二成分流体中に懸濁した球状粒子の抗力係数を議論する。強吸着における臨界吸着に伴うスケーリング挙動を捉えるため、Local renormalized functional theoryの枠組みを採用する。従来の理論研究では、大きなバルク相関長を持つ系において、積分方程式として表される流体方程式と化学ポテンシャル方程式を解く際に数値的困難に直面した。本研究では、コンパクト化された半径座標を用いて流体力学方程式を常微分方程式群として再構成することで、これらの制限を克服した。この手法により、より安定した数値計算が可能となり、粒子から離れた領域における適切な境界条件の設定が容易になった。その結果、従来の研究よりも広いバルク相関長範囲にわたる抗力係数の計算に成功し、実験データとの比較を行う。
藪中 俊介; Delamotte, B.*
no journal, ,
We show that at 
and below its upper critical dimension, 
, the critical and tetracritical behaviors of the models are associated with the same renormalization group fixed point (FP) potential. Only their derivatives make them different with the subtleties that taking their limit and deriving them do not commute and that two relevant eigenperturbations show singularities. This invalidates both the - and the - expansions. We also show how the Bardeen-Moshe-Bander line of tetracritical FPs at and 
can be understood from a finite- analysis.
Lu, M.-J.*; 藪中 俊介
no journal, ,
Traveling waves are a characteristic feature of active polar systems, observed both in theoretical models and in experiments on cohesive tissues, and are commonly interpreted through linear stability analyses. An important open question is whether traveling waves can persist as asymptotic dynamical attractors in active polar media once transverse degrees of freedom and topological defects are permitted. In this work, we address this question by comparing one- and two-dimensional active polar models within a unified theoretical and numerical framework. In one dimension, traveling waves arise robustly and are well characterized by their selected wavelength and propagation speed. In two dimensions, instead, depending on initial conditions and activity strength, the system relaxes into one of two statistically steady states: an ordered but non-propagating configuration, or a defect-rich active turbulent state. Using steady-state diagnostics based on kymographs and cross-correlation drift measurements, we demonstrate that apparent local motion in two dimensions does not correspond to net wave propagation.
