On massive sets for subordinated random walks

Abstract

We study massive (reccurent) sets with respect to a certain random walk $S_α$ defined on the integer lattice $\mathbb{Z} ^d$, $d=1,2$. Our random walk $S_α$ is obtained from the simple random walk $S$ on $\mathbb{Z} ^d$ by the procedure of discrete subordination. $S_α$ can be regarded as a discrete space and time counterpart of the symmetric $α$-stable Lévy process in $\mathbb{R}^d$. In the case $d=1$ we show that some remarkable proper subsets of $\mathbb{Z}$ , e.g. the set $\mathcal{P}$ of primes, are massive whereas some proper subsets of $\mathcal{P}$ such as Leitmann primes $\mathcal{P}_h$ are massive/non-massive depending on the function $h$. Our results can be regarded as an extension of the results of McKean (1961) about massiveness of the set of primes for the simple random walk in $\mathbb{Z}^3$. In the case $d=2$ we study massiveness of thorns and their proper subsets.