Persistence of invertibility on the Wiener space

Abstract

Let $(W,H,\mu)$ be the classical Wiener space, assume that $U=I_W+u$ is an adapted perturbation of identity where the perturbation $u$ is an equivalence class w.r.to the Wiener measure. We study several necessary and sufficient conditions for the almost sure invertibility of such maps. In particular the subclass of these maps who preserve the Wiener measure are characterized in terms of the corresponding innovation processes. We give the following application: let $U$ be invertible and let $\tau$ be stopping time. Define $U^\tau$ as $I_W+u^\tau$ where $u^\tau$ is given by $$ u^\tau(t,w)=\int_0^t 1_{[0,\tau(w)]}(s)\dot{u}_s(w)ds\,. $$ We prove that $U^\tau$ is also almost surely invertible. Note that this has immediate applications to stochastic differential equations.