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arXiv 1507.06008math.PR
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动态随机环境中的抛物型Anderson模型:随机电导

Parabolic Anderson model in a dynamic random environment: random conductances

Dirk Erhard, Frank den Hollander, Gregory Maillard

摘要:

抛物型安德森模型定义为偏微分方程\partial u(x,t)/ \partial t = κΔu(x,t)+ ε(x,t)u(x,t),x \in \Z^d,t \geq 0,其中κ \in [0,\infty)是扩散常数,Δ是离散拉普拉斯算子,ε是驱动方程的动态随机环境。初始条件u(x,0)=u_0(x),xPDMATHABMN \Z^d,被认为是非负的和有界的。抛物型安德森方程的解描述了一个粒子场的演化,这些粒子进行独立的简单随机行走,并具有二元分支:粒子以2dκ的速率跳跃,以\vee 0的速率分裂成两个,并以(-<$)\vee 0的速率死亡。我们的重点是李雅普诺夫指数λ_p(κ)= \lim_{t\to\infty} \frac{1}{t} \log \E([u(0,t)]^p)^{1/p},pPDMATHABMN \N,和λ_0(κ)= \lim_{t\to\infty} \frac{1}{t} \log u(0,t).我们研究了当κΔ被Δ^ \cK取代时会发生什么,其中\cK = \{ \mathcal{K}(x,y)\colon \,x,y \in \Z^d,\,x \sim y\}是取代均匀模型中常数电导κ的相邻位点之间的随机电导的集合。我们证明了相关的退火李雅普诺夫指数由公式λ_p(\cK)= \sup \{λ_p(κ)\colon,κ \in \Supp(\cK)\}给出,其中\Supp(\cK)是\cK -域所取的值的集合.我们还表明,对于相关的淬火李雅普诺夫指数,这个公式只提供了一个下限。我们的证明是有效的三个类的可逆性,并为所有\cK满足一定的聚类性质,即,有任意大的球,\cK几乎是常数,并接近任何值在\Supp(\cK)。我们的结果表明,李雅普诺夫指数是由\cK的那些口袋控制的,在这些口袋中,电导接近于使均匀环境中的增长最大化的值。

英文摘要:

The parabolic Anderson model is defined as the partial differential equation \partial u(x,t)/\partial t = κΔu(x,t) + ξ(x,t)u(x,t), x\in\Z^d, t\geq 0, where κ\in [0,\infty) is the diffusion constant, Δis the discrete Laplacian, and ξis a dynamic random environment that drives the equation. The initial condition u(x,0)=u_0(x), x\in\Z^d, is taken to be non-negative and bounded. The solution of the parabolic Anderson equation describes the evolution of a field of particles performing independent simple random walks with binary branching: particles jump at rate 2dκ, split into two at rate ξ\vee 0, and die at rate (-ξ) \vee 0. Our focus is on the Lyapunov exponents λ_p(κ) = \lim_{t\to\infty} \frac{1}{t} \log \E([u(0,t)]^p)^{1/p}, p \in \N, and λ_0(κ) = \lim_{t\to\infty} \frac{1}{t}\log u(0,t). We investigate what happens when κΔis replaced by Δ^\cK, where \cK = \{\mathcal{K}(x,y)\colon\,x,y\in\Z^d,\,x \sim y\} is a collection of random conductances between neighbouring sites replacing the constant conductances κin the homogeneous model. We show that the associated annealed Lyapunov exponents are given by the formula λ_p(\cK) = \sup\{λ_p(κ) \colon\,κ\in\Supp(\cK)\}, where \Supp(\cK) is the set of values taken by the \cK-field. We also show that for the associated quenched Lyapunov exponent this formula only provides a lower bound. Our proof is valid for three classes of reversible ξ, and for all \cK satisfying a certain clustering property, namely, there are arbitrarily large balls where \cK is almost constant and close to any value in \Supp(\cK). What our result says is that the Lyapunov exponents are controlled by those pockets of \cK where the conductances are close to the value that maximises the growth in the homogeneous setting.

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