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Infinite log-concavity of the Taylor coefficients of the Riemann xi-function

Combinatorics · Submitted 4 Oct 2026 · 29 references

Pith's verdict: Genuine result: unconditional strict infinite log-concavity of the xi-function coefficients, resolving Zhu's conjecture, with the real risk confined to the finite interval certificate rather than the analytic chain.

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arXiv ID2610.04972 (version 1)
Pith IDAWOGTOG6, Pith's permanent record of this paper and its review
CitationJianxi Mao, Yanxin Liu. "Infinite log-concavity of the Taylor coefficients of the Riemann xi-function." arXiv:2610.04972 (2026). https://pith.science/paper/AWOGTOG6
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The paper

The paper claims

This paper proves that the sequence of even Taylor coefficients of the Riemann xi-function at its central point, λ_n = ξ^{(2n)}(1/2)/(2n)!, is strictly infinitely log-concave, and it does so without assuming the Riemann hypothesis.

The reading

The paper proves that the sequence of even Taylor coefficients of the Riemann xi-function at its central point, λ_n = $ξ^{{(2n)}}$(1/2)/(2n)!, is strictly infinitely log-concave, and it does so without assuming the Riemann hypothesis. Since RH is equivalent to F(x) = ξ(1/2 + √x) lying in the Laguerre–Pólya class, and membership in that class forces infinite log-concavity, the new content is that the property holds unconditionally, independent of where the zeros lie. The result settles Zhu's 2023 conjecture, which had previously been pushed only to 6-log-concavity.

What carries the argument

The load-bearing object is the logarithmic-ratio sequence g_{m,n} = log r_{m,n}, evolving under g_{m+1,n} = 2g_{m,n} − Δ²h(g_{m,n}), h(t) = log(1−$e^{{−t}}$), which turns each application of the Turán operator L into a convexity-preserving second-difference step. The initial datum comes from a saddle-point estimate of the integral H defining the ξ-coefficients: on |arg z| ≤ π/4, |z| ≥ 4000, |H/H* − 1| ≤ 30/T, where the saddle is the Lambert W point w = W(2z/π) and H* is an explicit closed form; this yields the leading term Q(z) = 2w/(z(1+w)) for g_0 with error 20/n². Iteration on nested disks keeps positivity, and the golden-ratio threshold (3+√5)/2 is the fixed point of r ↦ (r−1)², so crossing it once locks in infinite log-concavity for all higher iterates.

Extended reading notes

Core claim

The central claim is Theorem 1.1: for F(x) = ξ(1/2 + √x) = Σ λ_n x^n with λ_n = $ξ^{{(2n)}}$(1/2)/(2n)!, one has (L^m λ)_n > 0 for all m,n ≥ 0, so the sequence is strictly infinitely log-concave. The proof works with logarithmic ratios g_{m,n} = log r_{m,n}, where r_{m,n} = A²_{m,n}/(A_{m,n-1}A_{m,n+1}) and A = L^m λ; positivity of g is exactly log-concavity at iteration m. These ratios propagate by the recurrence g_{m+1,n} = 2g_{m,n} − Δ²h(g_{m,n}) with h(t) = log(1−$e^{{−t}}$). The initial ratios are estimated from an integral representation Λ(z) = H(z)/Γ(2z+1) for λ_n, using a saddle-point estimate with the Lambert W function as saddle: |H/H* − 1| ≤ 30/T on the sector |arg z| ≤ π/4, |z| ≥ 4000, which yields |g_0(z) − Q(z)| ≤ 20/n² with Q(z) = 2w/(z(1+w)), w = W(2z/π). The iterates are then controlled on successively smaller disks, and the ratio r_{τ(n),n} is shown to exceed the golden-ratio threshold (3+√5)/2 at a finite τ(n): at τ(n) = ⌈log₂n⌉ for n ≥ 12000 and at m = 14 for the finitely many n below 12000 (the latter by certified interval arithmetic). A closure lemma shows that once r ≥ (3+√5)/2 holds at one iteration, it persists forever, because (r−1)² ≥ r exactly in that range.

Load-bearing premise

The proof rests on the explicit saddle-point estimate |H(z)/H*(z) − 1| ≤ 30/T (T ≥ 630) and its propagated consequence |g_0(z) − Q(z)| ≤ 20/n² on the disk |z − n| ≤ n/2, together with the computer certification that r_{14,n} > 10 for n ≤ 12000; if any stated constant margin fails, or the interval-arithmetic certificate is wrong, the split between the analytic range (n ≥ 12000) and the finite range collapses.

Editorial extensions

If this is right

  • Every finite iterate of the Turán operator L applied to (λ_n) yields a positive sequence, so all finite-order Turán inequalities for the even Taylor coefficients of ξ at 1/2 hold unconditionally.
  • Zhu's 2023 conjecture is resolved: infinite log-concavity holds without RH, strengthening Brändén's conditional result into an unconditional statement.
  • The proof exhibits a reusable template — an analytic saddle estimate on an infinite range, a certified finite check on the remaining range, and a golden-ratio closure lemma — giving a practical route to infinite log-concavity for other moment-like sequences.
  • Infinite log-concavity is strictly weaker than RH, so this property is decoupled from the location of the zeros of ξ; it holds whether or not they line up on the critical line.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The closure lemma suggests a general criterion: any coefficient sequence that can be analytically interpolated and shown to satisfy r_{τ(n),n} > (3+√5)/2 at finitely many indices is infinitely log-concave; the same scheme could certify other sequences (partition numbers, other moment sequences) once a strong-ratio bound is available.
  • The saddle-point estimate |H/H* − 1| ≤ 30/T also gives an explicit zero-free region for H and quantitative control on the coefficients, a bonus tool that could be reused for other questions about ξ.
  • The golden-ratio threshold is probably not sharp; a smaller threshold would shorten the finite verification and could push the analytic/finite boundary down from n = 12000.
Original abstract

The Riemann hypothesis is equivalent to $F(x)$ belonging to the Laguerre--P\'olya class. Br\"and\'en [J. Reine Angew. Math., 2011] proved that if an entire function in the Laguerre--P\'olya class has nonnegative Taylor coefficients, then its coefficient sequence is infinitely log-concave. Consequently, the Riemann hypothesis implies the infinite log-concavity of $(\lambda_n)_{n\ge0}$. In this paper, we prove that the sequence $(\lambda_n)_{n\ge0}$ is strictly infinitely log-concave. This resolves a conjecture of Zhu [Math. Z., 2023]. The proof combines explicit complex-analytic estimates for the iterated logarithmic ratios, rigorous interval arithmetic for a finite range of indices, and a global closure argument.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-10-06: 1 request, 5,529 input tokens.

What the abstract itself states, as probabilities: claims first 0.09 · states limitation 0.08 · human participants 0.01 · controlled comparison 0.01 · randomized assignment 0.01 · states quantitative result 0.11 · compares with prior results 0.80 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

The Riemann hypothesis is equivalent to $F(x)$ belonging to the Laguerre--P\'olya class. Br\"and\'en [J. Reine Angew. Math., 2011] proved that if an entire function in the Laguerre--P\'olya class has nonnegative Taylor coefficients, then its coefficient sequence is infinitely log-concave. Consequently, the Riemann hypothesis implies the infinite log-concavity of $(\lambda_n)_{n\ge0}$. In this paper, we prove that the sequence $(\lambda_n)_{n\ge0}$ is strictly infinitely log-concave. This resolves a conjecture of Zhu [Math. Z., 2023]. The proof combines explicit complex-analytic estimates for the iterated logarithmic ratios, rigorous interval arithmetic for a finite range of indices, and a global closure argument.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 The Riemann hypothesis is equivalent to $F(x)$ belonging to the Laguerre--P\'olya class. background 1.00 0.05 0.03 asserted 1.00
s1 Br\"and\'en [J. Reine Angew. background 0.99 0.03 0.01 unclear 0.98
s2 Math., 2011] proved that if an entire function in the Laguerre--P\'olya class has nonnegative Taylor coefficients, then its coefficient sequence is infinitely log-concave. background 1.00 0.03 0.03 asserted 1.00
s3 Consequently, the Riemann hypothesis implies the infinite log-concavity of $(\lambda_n)_{n\ge0}$. background 0.67 0.11 0.07 asserted 0.98
s4 In this paper, we prove that the sequence $(\lambda_n)_{n\ge0}$ is strictly infinitely log-concave. result 0.85 0.97 0.94 asserted 1.00
s5 This resolves a conjecture of Zhu [Math. Z., 2023]. interpretation 0.48 0.69 0.13 asserted 1.00
s6 The proof combines explicit complex-analytic estimates for the iterated logarithmic ratios, rigorous interval arithmetic for a finite range of indices, and a global closure argument. method 1.00 0.92 0.03 asserted 0.97

What kind of paper the classifier reports this is: theoretical result 1.00 · evidence from proof or derivation 1.00.

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Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

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