Coarsening, nucleation, and the marked Brownian web

Coarsening on a one-dimensional lattice is described by the voter model or equivalently by coalescing (or annihilating) random walks representing the evolving boundaries between regions of constant color and by backward (in time) coalescing random walks corresponding to color genealogies. Asymptotics for large time and space on the lattice are described via a continuum space-time voter model whose boundary motion is expressed by the Brownian web (BW) of coalescing forward Brownian motions. In this paper, we study how small noise in the voter model, corresponding to the nucleation of randomly colored regions, can be treated in the continuum limit. We present a full construction of the continuum noisy voter model (CNVM) as a random quasicoloring of two-dimensional space time and derive some of its properties. Our construction is based on a Poisson marking of the backward BW within the double (i.e., forward and backward) BW.