Exceptional times for the instantaneous propagation of superprocess

Abstract

For a Dawson-Watanabe superprocess $X$ on $\mathbb{R}^d$, it is shown in Perkins (1990) that if the underlying spatial motion belongs to a certain class of L\'evy processes that admit jumps, then with probability one the closed support of $X_t$ is the whole space for almost all $t>0$ before extinction, the so-called ``instantaneous propagation'' property. In this paper for superprocesses on $\mathbb{R}^1$ whose spatial motion is the symmetric stable process of index $\alpha \in (0,2/3)$, we prove that there exist exceptional times at which the support is compact and nonempty. Moreover, we show that the set of exceptional times is dense with full Hausdorff dimension. Besides, we prove that near extinction, the support of the superprocess is concentrated arbitrarily close to the distinction point, thus upgrading the corresponding results in Tribe (1992) from $\alpha \in (0,1/2)$ to $\alpha \in (0,2/3)$, and we further show that the set of such exceptional times also admits a full Hausdorff dimension.