Density behaviour related to Lévy processes

Abstract

Let $p_t(x)$, $f_t(x)$ and $q_t^{\ast }(x)$ be the densities at time $t$ of a real Lévy process, its running supremum and the entrance law of the reflected excursions at the infimum. We provide relationships between the asymptotic behaviour of $p_t(x)$, $f_t(x)$ and $q_t^{\ast }(x)$, when $t$ is small and $x$ is large. Then for large $x$, these asymptotic behaviours are compared to this of the density of the Lévy measure. We show in particular that, under mild conditions, if $p_t(x)$ is comparable to $t\nu (x)$, as $t\to 0$ and $x\to \infty$, then so is $f_t(x)$.

25 pages