On the threshold of spread-out contact process percolation

Abstract: We study the stationary distribution of the (spread-out) $d$-dimensional contact process from the point of view of site percolation. In this process, vertices of $\mathbb{Z}^d$ can be healthy (state 0) or infected (state 1). With rate one infected sites recover, and with rate $\lambda$ they transmit the infection to some other vertex chosen uniformly within a ball of radius $R$. The classical phase transition result for this process states that there is a critical value $\lambda_c(R)$ such that the process has a non-trivial stationary distribution if and only if $\lambda > \lambda_c(R)$. In configurations sampled from this stationary distribution, we study nearest-neighbor site percolation of the set of infected sites; the associated percolation threshold is denoted $\lambda_p(R)$. We prove that $\lambda_p(R)$ converges to $1/(1-p_c)$ as $R$ tends to infinity, where $p_c$ is the threshold for Bernoulli site percolation on $\mathbb{Z}^d$. As a consequence, we prove that $\lambda_p(R) > \lambda_c(R)$ for large enough $R$, answering an open question of Liggett and Steif in the spread-out case.