Lipschitz cutset for fractal graphs and applications to the spread of infections

Abstract

We consider the fractal Sierpiński gasket or carpet graph in dimension $d\ge 2,$ denoted by $G$. At time $0$, we place a Poisson point process of particles onto the graph and let them perform independent simple random walks, which in this setting exhibit sub-diffusive behaviour. We generalise the concept of particle process dependent Lipschitz percolation to the (coarse graining of the) space-time graph $G\times \mathbb{R}$, where the opened/closed state of space-time cells is measurable with respect to the particle process inside the cell. We then provide an application of this generalised framework and prove the following: if particles can spread an infection when they share a site of $G$, and if they recover independently at some rate $\gamma >0$, then if $\gamma$ is sufficiently small, the infection started with a single infected particle survives indefinitely with positive probability.

Minor corrections, 1 figure updated