REVIEW 5 minor 44 references
Non-vanishing uniqueness threshold for hyperbolic Poisson-Voronoi percolation in dimension at least three
T0 review · 0 major / 5 minor · reviewed 2026-08-01 · deepseek-v4-flash
Pith's one-line read A lower bound holds for the uniqueness threshold in hyperbolic Voronoi percolation
desk verdict This paper resolves an open question of Grebík and Recke with a genuinely new reduced-path technique, and the proof largely holds up under scrutiny. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The key object is the 'reduced path': a subsequence of a black Delaunay path that is shortcut-free and whose 'normal' edges have Gabriel balls with controlled overlap. The Gabriel ball of two points is the ball with the geodesic midpoint as centre and radius equal to half their distance; a Delaunay edge requires this ball to contain no Poisson point. The machinery works by showing the expected number of reduced paths in the dependent graph is no larger than the expected number of shortcut-free paths in an independent-edge model, using the exponential overlap decay of equal hyperbolic balls to redistribute costs over the path. The independent model's edge probabilities decay as a power of a g
What would settle it
Find, for some d≥3, an intensity λ and a p smaller than the claimed uniform lower bound such that the connection probability between two points at hyperbolic distance h does not tend to zero as h→∞ — for instance by simulating the model and measuring whether a fixed point reaches arbitrarily distant targets with positive probability at small p. A single such pair (λ,p) would contradict Theorem 1. Alternatively, compute p_u(λ) exactly at a fixed small λ and show it is zero.
Extended reading notes
Core claim
The central claim is Theorem 1: inf_{λ>0} p_u(λ)>0 for Poisson-Voronoi percolation on H^d with d≥3. More precisely there is a p0=p0(d)>0 such that for all p≤p0 and all λ>0 the connection probability between two far-apart points decays to zero with their distance, and consequently there is almost surely no unique unbounded black cluster. The paper establishes this by bounding the probability that a pair of points are adjacent in the Delaunay graph by a doubly exponential function of their distance, introducing an independent-edge random connection model whose edge probabilities dominate this bound and are exactly computable, and showing via specially constructed 'reduced paths' that expected
Load-bearing premise
The central geometric input is that in hyperbolic space the volume of the overlap of two equal balls decays exponentially in their separation; if that overlap decayed only polynomially (as it does in Euclidean space), the bound transferring independent-edge paths to dependent Delaunay paths would fail.
Editorial extensions
If this is right
- For every intensity λ>0 and every p below a dimension constant p0(d), the event of exactly one unbounded black cluster has probability zero.
- Connection probabilities between far-apart points in the Delaunay graph decay to zero uniformly in λ for p≤p0, so the uniqueness threshold satisfies p_u(λ)≥p0 for all λ.
- The hyperbolic plane (where the threshold tends to 1) and product spaces (where it tends to 0) are both separated from H^d with d≥3, which has a threshold uniformly bounded away from 0.
- The proof yields effective, though not sharp, constants, so a quantitative lower bound on p_u(λ) could in principle be extracted for any fixed dimension.
Reading between the lines
- The exponential overlap estimate is the load-bearing geometric input: a space whose equal-ball intersections decay only polynomially (Euclidean space, product spaces) would not admit this comparison, suggesting the uniform positive threshold is a genuinely negatively-curved phenomenon.
- A natural next target is determining whether lim_{λ→0} p_u(λ) exists; the techniques here give upper bounds on connection probabilities but not the asymptotic value, and could be sharpened by choosing the independent-edge probabilities closer to the true Delaunay edge probabilities.
- The reduced-path construction is a general scheme for handling path dependencies in geometric graphs; it could plausibly be transferred to site percolation on Delaunay complexes of other negatively curved spaces or to non-amenable Cayley graphs built from hyperbolic isometries, though that transfer would require re-proving the overlap controls.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper proves that for Poisson-Voronoi percolation on hyperbolic space H^d, d≥3, the uniqueness threshold satisfies inf_{λ>0} p_u(λ)>0. The proof uses the standard characterization: for a small dimension-dependent p_0 and all λ≤1, the connection probability between two far-away points tends to zero, so p_0≤p_u(λ); for λ≥1, a separate coarse-graining argument gives a uniform positive lower bound on p_c(λ), hence on p_u(λ). The main technical work is an independent-edge model with edge probabilities P(z,w) given by (23), a bound on the expected number of shortcut-free paths (Proposition 10), and a reduced-path construction (Section 3.5) showing that any black Delaunay path can be compressed so that the expected number of reduced paths is at most the independent-edge path count. The reduction uses the exponential decay of overlap volume for equal hyperbolic balls (Lemma 9). All auxiliary lemmas are proved, including a self-contained proof of the Gracar–Lüchtrath–Mörters-type bound (Lemma 12) and a new elementary proof of the positive high-intensity percolation threshold (Proposition 23).
Significance. The result answers an open question of Grebík and Recke and establishes a strong contrast: whereas the uniqueness threshold vanishes at small intensities for Poisson-Voronoi percolation on products of hyperbolic spaces, it has a positive uniform lower bound in the rank-one case H^d, d≥3. The proof is original and essentially self-contained; the reduced-path technique for transferring estimates from an independent-edge model to the dependent Delaunay graph is the most novel contribution and may be of independent interest. The paper also contains a self-contained proof of a positive percolation threshold for all sufficiently large intensities, replacing a black-box use of a deep result. I found no load-bearing errors; the main chain Lemma 6 → Proposition 10 → Lemma 15/Proposition 14 → Corollaries 20–21 → Theorem 1 is sound.
minor comments (5)
- [Lemma 16] In the proof of Lemma 16, the displayed chain ending in '=14x' appears to be a numerical typo; the lower bound is actually 16.5x. The subsequent conclusion dist(c_ℓ,c_i)>14x remains valid, so this is purely presentational.
- [Abstract/§1] The statement attributing p_u(λ)≤1/2 to an unpublished argument of D'Achille and Curien is not verifiable from the cited literature. Since this result is not used in the proof, please either replace it by a public reference or clearly mark it as context not needed for the theorem.
- [Appendix A.6, Proposition 23] In the paragraph 'We claim there is no infinite path...', the sentence 'Letting n→∞ and using (47), this probability is zero' is terse. Spell out that an infinite bad cluster contains, for every n, a chordless bad path of length n, whose even-indexed vertices have independent badness events.
- [Corollary 8] The first inequality in the proof uses that E and the E_i are decreasing in the white point configuration; adding one sentence on this monotonicity would improve readability.
- [Section 3.5 / Corollary 20] The definition of R_n(h) counts reduced paths whose internal vertices all have height <h; in the proof of Corollary 20 it is implicitly used that a connection to a point of height ≥h can be truncated at the first time the height exceeds h. This is correct, but it may be worth stating explicitly.
Circularity Check
No significant circularity: the proof is self-contained and does not reduce to its inputs by construction.
full rationale
The derivation chain for Theorem 1 is: Lemma 6/Corollary 8 bound Delaunay edge probabilities; Lemma 9 supplies the hyperbolic ball-overlap decay; the independent-edge model with kernel P is analyzed in Proposition 10; the reduced-path comparison (Lemma 15, Proposition 14) transfers the bound back to the Delaunay graph; Corollaries 20 and 21 convert the expectation bound into vanishing connection probabilities; and Propositions 22 and 23 turn this into the stated lower bound on p_u(λ). Every load-bearing auxiliary result is proved in the paper, including Lemma 12 (with a self-contained proof in Appendix A.3 despite the attribution to Gracar et al.), Lemma 9, Proposition 14, Proposition 22, and Proposition 23 (with an elementary proof in Appendix A.6). The kernel P(z,w) is chosen to dominate the true edge probability and is not fitted to the desired conclusion; the constant p_0 is selected only after the bound S_n(h) ≤ (c_1 p)^n P(Po(c_2 ln h) < n) is established. External results (Grebík–Recke, d'Achille et al., D'Achille–Curien, Bühler et al., Benjamini–Schramm) are contextual or non-load-bearing; in particular the unpublished D'Achille–Curien bound p_u ≤ 1/2 is not used in the proof. The only self-citation of Hansen–Müller serves to recall the Mecke formula, which is a standard external tool and not the target result. No equation or fitted parameter is shown to be equivalent by construction to the claimed theorem, so the derivation is not circular.
Assumptions & free parameters
free parameters (4)
- s0 =
chosen sufficiently large to satisfy (38); exact value unspecified
- x0 =
max(x1(δ), 10(d-1))
- delta =
sufficiently small; not given numerically
- A (Appendix A.6) =
large enough that Δ_A e^{-A/4}<1
assumptions (6)
- standard math Chernoff bound for Poisson and binomial random variables (Lemma 2).
- standard math Wendel's formula for i.i.d. rotationally invariant points (Lemma 4).
- standard math Mecke formula and Palm calculus for Poisson processes (Theorem 5).
- standard math Hyperbolic geometry facts: volume of balls is (1+o(1)) ω_{d-1} e^{(d-1)r}/2^{d-1}(d-1), balls in Poincaré models are Euclidean balls, hyperbolic cosine rule (Section 2.2).
- domain assumption Meester-Roy ergodicity: the event of exactly one unbounded cluster has probability 0 or 1.
- domain assumption Harris-FKG inequality for the two-type Poisson process (increasing in black, decreasing in white).
Cite this review
Pith. "Pith review of Non-vanishing uniqueness threshold for hyperbolic Poisson-Voronoi percolation in dimension at least three." pith.science (2026). https://pith.science/paper/VNOMTCNX
@misc{pith2026260717764,
author = {Pith},
title = {Pith review of: Non-vanishing uniqueness threshold for hyperbolic Poisson-Voronoi percolation in dimension at least three},
year = {2026},
howpublished = {\url{https://pith.science/paper/VNOMTCNX}},
note = {Machine review of arXiv:2607.17764}
}
abstract
We study the threshold for the existence of exactly one unbounded cluster for Poisson-Voronoi percolation on the $d$-dimensional hyperbolic space $\mathbb{H}^d$ for $d\geq 3$. By recent results of Greb\'ik and Recke and d'Achille et al., this "uniqueness threshold" $p_u(\lambda)$ tends to zero as the intensity $\lambda$ of the underlying Poisson point process tends to zero, for Poisson-Voronoi percolation defined on an ambient space from a family of geometric spaces that includes Cartesian products $\mathbb{H}^{d_1}\times\dots\times\mathbb{H}^{d_k}$ with $k,d_1,\dots,d_k\geq 2$. In contrast, for Poisson-Voronoi percolation on the hyperbolic plane $\mathbb{H}^2$, Benjamini and Schramm have shown that $p_u(\lambda)$ tends to one as $\lambda$ tends to zero, and $p_u(\lambda)>1/2$ for all $\lambda>0$. An unpublished argument of D'Achille and Curien shows that for Poisson-Voronoi percolation on $\mathbb{H}^d$ with $d\geq 3$, the uniqueness threshold satisfies $p_u(\lambda)\leq 1/2$ for all $\lambda>0$. Here we will show that $\inf_{\lambda>0}p_u(\lambda)>0$ for Poisson-Voronoi percolation on $\mathbb{H}^d$ with $d\geq 3$. This answers a question of Greb\'ik and Recke.
Figures
Reference graph
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As observed earlier, the lemma statement follows.■ 37 A.4 Proof of Proposition 13
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