Within the framework of the renormalization group approach in the stochastic model of fully developed turbulence, the $β$-function has been calculated in the fourth order of perturbation theory for high-dimensional spaces $d \rightarrow \infty$. The position of the fixed point of the renormalization group in the fourth order of the $\varepsilon$-expansion has been determined, and the index $ω$, which defines the infrared stability of this point, has been calculated. We demonstrate the possibility of significantly reducing the number of Feynman diagrams through mutual cancellation. The results obtained allow us to find the four terms of the $\varepsilon$-expansion of the index $ω$: $$
ω= 2\,\varepsilon + \frac{2}{3}\,\varepsilon^2 + \frac{10}{9}\,\varepsilon^3 + \frac{56}{27}\,\varepsilon^4. $$
Anomalous scaling and large-scale anisotropy in magnetohydrodynamic turbulence: Two-loop renormalization-group analysis of the Kazantsev--Kraichnan kinematic model
On Functional and Holographic Renormalization Group Methods in Stochastic Theory of Turbulence
A nonlocal quantum-field model is constructed for the system of hydrodynamic equations for incompressible viscous fluid (the stochastic Navier--Stokes (NS) equation and the continuity equation). This model is studied by the following two mutually parallel methods: the Wilson--Polchinski functional renormalization group method (FRG), which is based on the exact functional equation for the generating functional of amputated connected Green's functions (ACGF), and the Heemskerk--Polchinski holographic renormalization group method (HRG), which is based on the functional Hamilton--Jacobi (HJ) equat…
Two-loop calculation of anomalous kinetics of the reaction $A + A \rightarrow\varnothing$ in randomly stirred fluid
研究了由随机纳维-斯托克斯方程产生的随机速度场作用下的单粒子湮灭反应$A + A \rightarrow\varnothing$。利用重整化群分析了密度和速度涨落对系统长时间行为的综合影响。由于速度涨落对反应常数的直接影响只表现在双圈阶上,因此在双圈近似下,用双参数$(ε, Δ)$展开计算了重整化群的所有稳定不动点及其稳定区域.提出了一个重正化的数密度积分微分方程,该方程考虑了次首阶密度和速度涨落的影响。在均匀系统中计算了微扰理论中该方程的解。
Spin functional renormalization group for quantum Heisenberg ferromagnets: Magnetization and magnon damping in two dimensions
我们使用我们两人最近开发的自旋泛函重整化群[J. Krieg和P. Kopietz,Phys. Rev. B $\bf{99}$,060403(R)(2019)]来计算由于量子海森堡铁磁体的经典纵向波动引起的磁化强度$M ( H , T )$和磁振子的阻尼。为了保证磁场$H \rightarrow 0$为零时,自旋旋转不变性自发破缺时磁振子谱是无隙的,我们用Ward恒等式表示磁振子自能的磁化强度.在二维中,我们的方法正确地预测了在有限温度下$T$的$H=0$的长程磁序的情况下。磁振子谱则呈现出一个能隙,我们由此得到横向关联长度。我们还计算了磁振子的波函数重整化因子。作为一个数学副产品,我们推导出一个递归形式的广义威克定理的自旋算符在频率空间,这有利于计算任意时间有序的连接关联函数的孤立自旋在磁场。