Abstract

We study the Siegel--Veech transform on the Poincaré section for the horocycle flow consisting of lattice surfaces with a visible horizontal holonomy vector of length at most one. We compute its first moment and derive formulas for higher and factorial moments with respect to the section's induced ergodic invariant probability measure, which is not supported on a periodic orbit. We emphasize these formulas in the case of the square torus of unit area and, as an application, use its first-moment formula to recover the Boca--Zaharescu pair-correlation density for Farey fractions.

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Audited against arXiv v1

Not a correctness certificate. A green “no issues found” result may include yellow suspected typos or minor formal issues that do not affect substantive soundness. It means this audit found no unresolved substantive error under the stated criteria; it does not replace expert scrutiny or formal verification.

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Detailed mathematical audit

Generated October 24, 2026
01Statements4 reported findingsNo statement issues found

The first, higher, and factorial moment formulas follow from the parabolic-orbit decomposition of visible holonomy vectors. Their modular specializations are correct, and the first-moment formula yields the stated Farey pair-correlation density. One auxiliary finite-QQ identity needs the harmless qualifier “for all sufficiently large QQ.”

Theorems 1.1–1.3No issue found

The cross-sectional first and second moments have the stated densities

PDF pp. 3–5 and 9–18 · arXiv:2609.33788v1

At each height ζ\zeta, visible vectors split into ϕ(ζ)\phi(\zeta) residue classes under the cusp translation. Summing the common parabolic shift tiles the horizontal line, and the change y=ζ/sy=\zeta/s supplies the factor y−2y^{-2}. For two vectors, fixing their heights, residue classes, and relative shift fixes their determinant and leaves the same one-dimensional unfolding. In the modular case, regrouping primitive residue classes by n=Ak−Bjn=Ak-Bj gives exactly the coefficient Φj,k(n)\Phi_{j,k}(n).

Theorems 5.1, 5.3, and 5.4No issue found

The higher and factorial moment formulas follow from the same determinant parametrization

PDF pp. 18–22 · arXiv:2609.33788v1

Using the first vector as the integration coordinate leaves one common parabolic shift and records every other vector by its height and determinant with the first. Lemma 5.2 correctly expresses every pairwise determinant as (ζℓDm−ζmDℓ)/ζ1(\zeta_\ell D_m-\zeta_mD_\ell)/\zeta_1, so the displayed nonvanishing conditions are exactly pairwise distinctness for visible positive-height vectors. The modular congruences count precisely the admissible primitive residue tuples.

Theorem 6.3No issue found

The first moment recovers the Boca–Zaharescu pair-correlation density

PDF pp. 22–27 · arXiv:2609.33788v1

Future section returns at the periodic BCZ point encode the normalized positive Farey differences. The test transforms are uniformly bounded, Riemann integrable, and converge uniformly as NQ/Q2→3/π2N_Q/Q^2\to3/\pi^2, so periodic-orbit equidistribution applies. Inserting their defining function into the modular first-moment identity and changing xx to λ=3y/(π2x)\lambda=3y/(\pi^2x) produces the claimed totient sum and logarithm.

Lemma 6.2, equation (80)Suspected minor formal issue

The orbit-average identity is eventual, not valid for every QQ

PDF p. 25 · arXiv:2609.33788v1

The periodic BCZ orbit average also contains wrap-around pairs with i+r≥NQi+r\geq N_Q, whereas RQ(2)(H)R_Q^{(2)}(H) sums only pairs inside one copy of [0,1)[0,1). The proof itself shows these extra terms vanish once NQ/QN_Q/Q exceeds the upper endpoint of supp⁡(H)\operatorname{supp}(H). Thus equation (80) should read “for all sufficiently large QQ.” For example, at Q=1Q=1 a function with H(1)≠0H(1)\neq0 makes the orbit average nonzero while the within-period pair sum is empty. The corrected eventual identity is all that Theorem 6.3 uses.

02Proofs3 reported findingsNo proof issues found

The cusp unfolding, determinant bookkeeping, integrability arguments, factorial restrictions, and Farey/BCZ limiting calculation were checked through their proof-critical steps. Apart from the local quantifier correction in Lemma 6.2, the proofs are complete.

Theorem 3.1 and Corollary 3.4No issue found in the reviewed proof

The first-moment unfolding is exact

PDF pp. 9–12 · arXiv:2609.33788v1

For fixed ss, consecutive cusp translates produce adjacent intervals of length αζs\alpha\zeta s, so their tt-integrals cover R\mathbb R exactly once. Then ds=−ζy−2dyds=-\zeta y^{-2}dy cancels the prefactor 1/ζ1/\zeta. Compact support bounds the contributing heights and proves absolute integrability for signed test functions. For the square torus, α=1\alpha=1, J=NJ=\mathbb N, and ϕ=φ\phi=\varphi, yielding the density 2Φ(y)/y22\Phi(y)/y^2.

Theorems 4.1 and 4.4No issue found in the reviewed proof

Relative shifts and determinant data are counted without multiplicity

PDF pp. 12–18 · arXiv:2609.33788v1

The change (q1,q2)↔(q1,q1−q2)(q_1,q_2)\leftrightarrow(q_1,q_1-q_2) is bijective, and determinant invariance determines the second transformed vector from the first. In the modular regrouping, a residue pair contributes to determinant nn exactly when ak−bj≡n(modjk)ak-bj\equiv n\pmod{jk}; after that congruence, one free integer shift remains. Compact support bounds both heights and the determinant, so the signed formulas are absolutely integrable.

Lemmas 6.1–6.2 and Theorem 6.3Correct and complete after a minor formal correction

The Farey limit proof is complete after the stated eventual-identity correction

PDF pp. 24–27 · arXiv:2609.33788v1

A vector with transformed coordinates (x,y)(x,y) and 0<x≤10<x\leq1 returns after time y/xy/x, and the sum of BCZ return times is Q2(γi+r−γi)Q^2(\gamma_{i+r}-\gamma_i). Only finitely many primitive vectors can contribute uniformly for scaling constants near 3/π23/\pi^2, which proves boundedness, Riemann integrability, and uniform convergence of the transforms. Wrap-around terms disappear for all sufficiently large QQ, exactly the regime needed before taking the weak limit.

03Novelty0 reported findingsNo novelty concerns found

No non-novelty findings.

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Paper
arXiv:2609.33788v1
Authors listed
Albert Artiles
Audit date
October 24, 2026
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