Lower bounds for the density of locally elliptic Itô processes
Abstract
Description
We give lower bounds for the density $p_T(x,y)$ of the law of $X_t$, the solution of $dX_t=σ(X_t) dB_t+b(X_t) dt,X_0=x,$ under the following local ellipticity hypothesis: there exists a deterministic differentiable curve $x_t, 0\leq t\leq T$, such that $x_0=x, x_T=y$ and $σσ^*(x_t)>0,$ for all $t\in \lbrack 0,T].$ The lower bound is expressed in terms of a distance related to the skeleton of the diffusion process. This distance appears when we optimize over all the curves which verify the above ellipticity assumption. The arguments which lead to the above result work in a general context which includes a large class of Wiener functionals, for example, Itô processes. Our starting point is work of Kohatsu-Higa which presents a general framework including stochastic PDE's.
Published at http://dx.doi.org/10.1214/009117906000000458 in the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org)
Published at http://dx.doi.org/10.1214/009117906000000458 in the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org)