114 research outputs found
Discretisation of regularity structures
We introduce a general framework allowing to apply the theory of regularity
structures to discretisations of stochastic PDEs. The approach pursued in this
article is that we do not focus on any one specific discretisation procedure.
Instead, we assume that we are given a scale and a "black
box" describing the behaviour of our discretised objects at scales below
Asymptotics of the critical time in Wiener sausage percolation with a small radius
We consider a continuum percolation model on , where .The
occupied set is given by the union of independent Wiener sausages with radius
running up to time and whoseinitial points are distributed according to
a homogeneous Poisson point process.It was established in a previous work by
Erhard, Mart\'{i}nez and Poisat~\cite{EMP13} that (1) if is small enough
there is a non-trivial percolation transitionin occuring at a critical time
and (2) in the supercritical regime the unbounded cluster is unique.
In this paper we investigate the asymptotic behaviour of the critical time when
the radius converges to . The latter does not seem to be deducible from
simple scaling arguments. We prove that for , there is a positive
constant such that when and $c^{-1}r^{(4-d)/2}\leq t\_c(r) \leq c\
r^{(4-d)/2}d\geq 5r0$. We derive along the way
moment estimates on the capacity of Wiener sausages, which may be of
independent interest
The parabolic Anderson model in a dynamic random environment: basic properties of the quenched Lyapunov exponent
In this paper we study the parabolic Anderson equation \partial
u(x,t)/\partial t=\kappa\Delta u(x,t)+\xi(x,t)u(x,t), x\in\Z^d, t\geq 0, where
the u-field and the \xi-field are \R-valued, \kappa \in [0,\infty) is the
diffusion constant, and is the discrete Laplacian. 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 2d\kappa, split into two at rate \xi\vee 0, and die at
rate (-\xi)\vee 0. Our goal is to prove a number of basic properties of the
solution u under assumptions on that are as weak as possible. Throughout
the paper we assume that is stationary and ergodic under translations in
space and time, is not constant and satisfies \E(|\xi(0,0)|)<\infty, where \E
denotes expectation w.r.t. \xi. Under a mild assumption on the tails of the
distribution of \xi, we show that the solution to the parabolic Anderson
equation exists and is unique for all \kappa\in [0,\infty). Our main object of
interest is the quenched Lyapunov exponent
\lambda_0(\kappa)=\lim_{t\to\infty}\frac{1}{t}\log u(0,t). Under certain weak
space-time mixing conditions on \xi, we show the following properties:
(1)\lambda_0(\kappa) does not depend on the initial condition u_0;
(2)\lambda_0(\kappa)<\infty for all \kappa\in [0,\infty); (3)\kappa \mapsto
\lambda_0(\kappa) is continuous on [0,\infty) but not Lipschitz at 0. We
further conjecture:
(4)\lim_{\kappa\to\infty}[\lambda_p(\kappa)-\lambda_0(\kappa)]=0 for all
p\in\N, where \lambda_p
(\kappa)=\lim_{t\to\infty}\frac{1}{pt}\log\E([u(0,t)]^p) is the p-th annealed
Lyapunov exponent. Finally, we prove that our weak space-time mixing conditions
on \xi are satisfied for several classes of interacting particle systems.Comment: 50 pages. The comments of the referee are incorporated into the
paper. A missing counting estimate was added in the proofs of Lemma 3.6 and
Lemma 4.
Uniqueness and tube property for the Swiss cheese large deviations
We consider the simple random walk on the Euclidean lattice, in three
dimensions and higher, conditioned to visit fewer sites than expected, when the
deviation from the mean scales like the mean. The associated large deviation
principle was first derived in 2001 by van den Berg, Bolthausen and den
Hollander in the continuous setting, that is for the volume of a Wiener
sausage, and later taken up by Phetpradap in the discrete setting. One of the
key ideas in their work is to condition the range of the random walk to a
certain skeleton, that is a sub-sequence of the random walk path taken along an
appropriate mesoscopic scale. In this paper we prove that (i) the rate function
obtained by van den Berg, Bolthausen and den Hollander has a unique minimizer
over the set of probability measures modulo shifts, at least for deviations of
the range well below the mean, and (ii) the empirical measure of the skeleton
converges under the conditioned law, in a certain manner, to this minimizer. To
this end we use an adaptation of the topology recently introduced by Mukherjee
and Varadhan to compactify the space of probability measures
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