English

Nonamenable Poisson zoo

Probability 2025-05-13 v1 Mathematical Physics Group Theory math.MP

Abstract

In the Poisson zoo on an infinite Cayley graph GG, we take a probability measure ν\nu on rooted finite connected subsets, called lattice animals, and place i.i.d. Poisson(λ\lambda) copies of them at each vertex. If the expected volume of the animals w.r.t. ν\nu is infinite, then the whole GG is covered for any λ>0\lambda>0. If the second moment of the volume is finite, then it is easy to see that for small enough λ\lambda the union of the animals has only finite clusters, while for λ\lambda large enough there are also infinite clusters. Here we show that: 1. If GG is a nonamenable free product, then for ANY ν\nu with infinite second but finite first moment and any λ>0\lambda>0, there will be infinite clusters, despite having arbitrarily low density. 2. The same result holds for ANY nonamenable GG, when the lattice animals are worms: random walk pieces of random finite length. It remains open if the result holds for ANY nonamenable Cayley graph with ANY lattice animal measure ν\nu with infinite second moment. 3. We also give a Poisson zoo example ν\nu on Td×Z5\mathbb{T}_d \times \mathbb{Z}^5 with finite first moment and a UNIQUE infinite cluster for any λ>0\lambda>0.

Keywords

Cite

@article{arxiv.2505.07145,
  title  = {Nonamenable Poisson zoo},
  author = {Gábor Pete and Sándor Rokob},
  journal= {arXiv preprint arXiv:2505.07145},
  year   = {2025}
}

Comments

40 pages, 4 figures

R2 v1 2026-06-28T23:28:55.294Z