Extremal percolation probabilities among isotropic degree-two models

Let Cp\mathcal{C}_p be the class of probability distributions on Ω\Omega that are independent and identically distributed over the vertices, isotropic, and have expected degree equal to pp. For PCp\mathbf{P}\in\mathcal{C}_p, let θ(P)\theta(\mathbf{P}) denote its percolation probability, and let θpns–ew\theta^{\text{ns--ew}}_p and θpaon\theta^{\text{aon}}_p denote the percolation probabilities of the northsouth-eastwest and all-or-nothing models at parameter pp. Extremal-model conjecture. For every PCp\mathbf{P}\in\mathcal{C}_p,

θpns–ewθ(P)θpaon.\theta^{\text{ns--ew}}_p \geq \theta(\mathbf{P}) \geq \theta^{\text{aon}}_p.

This proposes that the northsouth-eastwest and all-or-nothing models are respectively extremal among isotropic, vertex-i.i.d. environments with a fixed expected degree. It is motivated by numerical observations and variance intuition, and remains an open problem.

Sources & referencesView supporting material

Primary source

David Coupier, Benoît Henry, Benedikt Jahnel and Jonas Köppl, “The Planar Lattice Two-Neighbor Graph Percolates”, arXiv:2412.20781 (2024).

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