No Arabic abstract
This article generalizes the small noise cutoff phenomenon to the strong solutions of the stochastic heat equation and the damped stochastic wave equation over a bounded domain subject to additive and multiplicative Wiener and Levy noises in the Wasserstein distance. For the additive noise case, we obtain analogous infinite dimensional results to the respective finite dimensional cases obtained recently by Barrera, Hogele and Pardo (JSP2021), that is, the (stronger) profile cutoff phenomenon for the stochastic heat equation and the (weaker) window cutoff phenomenon for the stochastic wave equation. For the multiplicative noise case, which is studied in this context for the first time, the stochastic heat equation also exhibits profile cutoff phenomenon, while for the stochastic wave equation the methods break down due to the lack of symmetry. The methods rely strongly on the explicit knowledge of the respective eigensystem of the stochastic heat and wave operator and the explicit representation of the stochastic solution flows in terms of stochastic exponentials.
In this work we first present the existence, uniqueness and regularity of the strong solution of the tidal dynamics model perturbed by Levy noise. Monotonicity arguments have been exploited in the proofs. We then formulate a martingale problem of Stroock and Varadhan associated to an initial value control problem and establish existence of optimal controls.
We consider a family of nonlinear stochastic heat equations of the form $partial_t u=mathcal{L}u + sigma(u)dot{W}$, where $dot{W}$ denotes space-time white noise, $mathcal{L}$ the generator of a symmetric Levy process on $R$, and $sigma$ is Lipschitz continuous and zero at 0. We show that this stochastic PDE has a random-field solution for every finite initial measure $u_0$. Tight a priori bounds on the moments of the solution are also obtained. In the particular case that $mathcal{L}f=cf$ for some $c>0$, we prove that if $u_0$ is a finite measure of compact support, then the solution is with probability one a bounded function for all times $t>0$.
We consider the stochastic heat equation with a multiplicative white noise forcing term under standard intermitency conditions. The main finding of this paper is that, under mild regularity hypotheses, the a.s.-boundedness of the solution $xmapsto u(t,,x)$ can be characterized generically by the decay rate, at $pminfty$, of the initial function $u_0$. More specifically, we prove that there are 3 generic boundedness regimes, depending on the numerical value of $Lambda:= lim_{|x|toinfty} |log u_0(x)|/(log|x|)^{2/3}$.
Existence and uniqueness of solutions to the stochastic heat equation with multiplicative spatial noise is studied. In the spirit of pathwise regularization by noise, we show that a perturbation by a sufficiently irregular continuous path establish wellposedness of such equations, even when the drift and diffusion coefficients are given as generalized functions or distributions. In addition we prove regularity of the averaged field associated to a Levy fractional stable motion, and use this as an example of a perturbation regularizing the multiplicative stochastic heat equation.
Let ${G_n}_{1}^{infty}$ be a sequence of non-trivial finite groups, and $widehat{G}_n$ denote the set of all non-isomorphic irreducible representations of $G_n$. In this paper, we study the properties of a random walk on the complete monomial group $G_nwr S_n$ generated by the elements of the form $(text{e},dots,text{e},g;text{id})$ and $(text{e},dots,text{e},g^{-1},text{e},dots,text{e},g;(i,n))$ for $gin G_n,;1leq i< n$. We call this the warp-transpose top with random shuffle on $G_nwr S_n$. We find the spectrum of the transition probability matrix for this shuffle. We prove that the mixing time for this shuffle is $Oleft(nlog n+frac{1}{2}nlog (|G_n|-1)right)$. We show that this shuffle presents $ell^2$-pre-cutoff at $nlog n+frac{1}{2}nlog (|G_n|-1)$. We also show that this shuffle exhibits $ell^2$-cutoff phenomenon with cutoff time $nlog n+frac{1}{2}nlog (|G_n|-1)$ if $|widehat{G}_n|=o(|G_n|^{delta}n^{2+delta})$ for all $delta>0$. We prove that this shuffle has total variation cutoff at $nlog n+frac{1}{2}nlog (|G_n|-1)$ if $|G_n|=o(n^{delta})$ for all $delta>0$.