Thomas Mountford

THE MOTION OF A SECOND CLASS PARTICLE FOR THE TASEP STARTING FROM A DECREASING SHOCK PROFILE

We prove a strong law of large numbers for the location of the second class particle in a totally asymmetric exclusion process when the process is started initially from a decreasing shock. This completes a study initiated in Ferrari and Kipnis [Ann. Inst. H. Poincare Probab. Statist. 13 (1995) 143-154].

Limit laws of transient excited random walks on integers

We consider excited random walks (ERWs) on Z with a bounded number of i.i.d. cookies per site without the non-negativity assumption on the drifts induced by the cookies. Kosygina and Zerner [15] have shown that when the total expected drift per site, delta, is larger than 1 then ERW is transient to the right and, moreover, for delta > 4 under the averaged measure it obeys the Central Limit Theorem. We show that when delta is an element of (2,4] the limiting behavior of an appropriately centered and scaled excited random walk under the averaged measure is described by a strictly stable law with parameter delta/2. Our method also extends the results obtained by Basdevant and Singh [2] for delta is an element of (1,2] under the non-negativity assumption to the setting which allows both positive and negative cookies.

An asymptotic result for Brownian polymers

We consider a model of the shape of a growing polymer introduced by Durrett and Rogers (Probab. Theory Related Fields 92 (1992) 337-349). We prove their conjecture about the asymptotic behavior of the underlying continuous process X-t (corresponding to the location of the end of the polymer at time t) for a particular type of repelling interaction function without compact support.

On large deviation regimes for random media models

The focus of this article is on the different behavior of large deviations of random subadditive functionals above the mean versus large deviations below the mean in two random media models. We consider the point-to-point first passage percolation time a(n) on Z(d) and a last passage percolation time Z(n). For these functionals, we have lim(n ->infinity) a(n)/n = v and lim(n ->infinity) Z(n)/n = mu. Typically, the large deviations for such functionals exhibits a strong asymmetry, large deviations above the limiting value are radically different from large deviations below this quantity. We develop robust techniques to quantify and explain the differences.

Crossing velocities for an annealed random walk in a random potential

We consider a random walk in an i.i.d. non-negative potential on the d-dimensional integer lattice. The walk starts at the origin and is conditioned to hit a remote location y on the lattice. We prove that the expected time under the annealed path measure needed by the random walk to reach y grows only linearly in the distance from y to the origin. In dimension 1 we show the existence of the asymptotic positive speed

Tightness for the interface of the one-dimensional contact process

We consider a symmetric, finite-range contact process with two types of infection; both have the same (supercritical) infection rate and heal at rate 1, but sites infected by Infection I are immune to Infection 2. We take the initial configuration where sites in (-infinity, 0] have Infection I and sites in [1, infinity) have Infection 2, then consider the process rho(t) defined as the size of the interface area between the two infections at time t. We show that the distribution of rho(t) is tight, thus proving a conjecture posed by Cox and Durrett in [Bernoulli 1 (1995) 343-370].

Feynman-Kac representation for the parabolic Anderson model driven by fractional noise

We consider the parabolic Anderson model driven by fractional noise: partial derivative/partial derivative t u(t,x) = k Delta u(t,x) + u(t,x)partial derivative/partial derivative t W(t,x) x is an element of Z(d), t >= 0, where k > 0 is a diffusion constant, Delta is the discrete Laplacian defined by Delta f (x) = 1/2d Sigma vertical bar y-x vertical bar=1 (f(Y) - f (0)), and {W(t,x) ; t > 0} x is an element of Z(d) is a family of independent fractional Brownian motions with Hurst parameter H is an element of (0,1), indexed by Z(d). We make sense of this equation via a Stratonovich integration obtained by approximating the fractional Brownian motions with a family of Gaussian processes possessing absolutely continuous sample paths. We prove that the Feynman-Kac representation u(t, x) = E-infinity [u(0) (X(t)) exp integral(t)(0) W(ds,X(t-s))], (1) is a mild solution to this problem. Here u(0) (y) is the initial value at site y is an element of Z(d), {X(t); t >= 0} is a simple random walk with jump rate f, started at x E Zd and independent of the family {W(t, x) ; t >= 0}(x is an element of Zd) and E-infinity is expectation withrespect to this random walk. We give a unified argument that works for any Hurst parameter H is an element of (0,1)

Supercritical behavior of asymmetric zero-range process with sitewise disorder

We establish necessary and sufficient conditions for weak convergence to the upper invariant measure for asymmetric nearest neighbour zero range processes with non homogeneous jump rates. The class of environments considered is close to that considered by Andjel, Ferrari, Guiol and Landim, while our class of processes is broader. We also give a simpler proof of a result of Ferrari and Sisko with weaker assumptions.

Supercriticality conditions for asymmetric zero-range process with sitewise disorder

We discuss necessary and sufficient conditions for the convergence of disordered asymmetric zero-range process to the critical invariant measures.

Anderson Polymer in a Fractional Brownian Environment: Asymptotic Behavior of the Partition Function

We consider the Anderson polymer partition function