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Author: Hesse, Marion × Publisher: Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik ×

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    The parabolic Anderson model on the hypercube
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2016) Avena, Luca; Gün, Onur; Hesse, Marion
    We consider the parabolic Anderson model (PAM) on the n-dimensional hypercube with random i.i.d. potentials. We parametrize time by volume and study the solution at the location of the k-th largest potential. Our main result is that, for a certain class of potential distributions, the solution exhibits a phase transition: for short time scales it behaves like a system without diffusion, whereas, for long time scales the growth is dictated by the principle eigenvalue and the corresponding eigenfunction of the Anderson operator, for which we give precise asymptotics. Moreover, the transition time depends only on the difference between the largest and the k-th largest potential. One of our main motivations in this article is to investigate the mutationselection model of population genetics on a random fitness landscape, which is given by the ratio of the solution of PAM to its total mass, with the field corresponding to the fitness landscape. We show that the phase transition of the solution translates to the mutation-selection model as follows: a population initially concentrated at the site of the k-th best fitness value moves completely to the site of the best fitness on time scales where the transition of growth rates happens. The class of potentials we consider involve the Random Energy Model (REM) of statistical physics which is studied as one of the main examples of a random fitness landscape.
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    The total mass of super-Brownian motion upon exiting balls and Sheu's compact support condition
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2013) Hesse, Marion; Kyprianou, Andreas
    We study the total mass of a d-dimensional super-Brownian motion as it first exits an increasing sequence of balls. The total mass process is a time-inhomogeneous continuous-state branching process, where the increasing radii of the balls are taken as the time-parameter. We characterise its time-dependent branching mechanism and show that it converges, as time goes to infinity, towards the branching mechanism of the total mass of a one-dimensional super-Brownian motion as it first crosses above an increasing sequence of levels. Our results identify the compact support criterion in Sheu (1994) as Grey's condition (1974) for the aforementioned limiting branching mechanism.