Joint Continuity of the Intersection Local Times of Markov Processes

Abstract

We describe simple conditions on the transition density functions of two independent Markov processes $X$ and $Y$ which guarantee the existence of a continuous version for the intersection local time, formally given by $\alpha (z, H) = \int_H\int \delta_z (Y_t - X_s) ds dt$. In the analogous case of self-intersections $\alpha$ can be discontinuous at $z = 0$. We develop a Tanaka-like formula for $\alpha$ and use this to show that the singular part of $\alpha (z,\lbrack 0, T\rbrack^2)$ as $z \rightarrow 0$ is given by $2\int^T_0 U(X_t - z, X_t) dt, a.s.$, where $U$ is the 1-potential of $X$.