arXiv:2608.00370v1

Continuity of measure-theoretic entropy for stochastic differential equations

Zhenxin Liu, Lixin Zhang

math.DSmath.PR28D2037A1037A3560H10

Abstract

For stochastic differential equations, we establish a relationship between the measure-theoretic entropy of the stochastic flow and the rate of volume growth of stable submanifolds under iteration. By combining the result of Kifer and Yomdin (1988), we show that under a suitable integrability condition, for systems with CC^{\infty} coefficients, the measure-theoretic entropy is upper semicontinuous with respect to the coefficients of SDEs.

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Audited against arXiv v1

Not a correctness certificate. A “Correct” result may include yellow typos or minor formal corrections 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 August 18, 2026
01Statements2 reported findingsContains wrong statements

The main upper-semicontinuity theorem is false under the stated C0C^0 convergence hypothesis. A rescaled compactly supported deterministic flow gives coefficients converging uniformly to zero while preserving positive metric entropy and concentrating its invariant measure at a zero-entropy fixed point. The two application theorems impose additional recurrence and nondegeneracy hypotheses, so this counterexample does not disprove them, but their printed proofs depend on the invalid general theorem and do not independently establish their conclusions.

Theorem 3.7Incorrect

Uniform convergence of coefficients does not imply upper semicontinuity of entropy

Pages 14–15 · Theorem 3.7 · arXiv:2608.00370v1

Choose a smooth compactly supported vector field XX on some Rd\mathbb R^d whose flow has a compact invariant probability measure ν\nu with positive time-one entropy; for example, embed a smooth suspension of a horseshoe in Euclidean space and extend its vector field through a tubular neighborhood with compact support. For εk0\varepsilon_k\downarrow0, set Ak(x)=εkX(x/εk)A_k(x)=\varepsilon_kX(x/\varepsilon_k) and Bk=0B_k=0, while A=B=0A=B=0. The flow satisfies Φkt(x)=εkΦXt(x/εk)\Phi_k^t(x)=\varepsilon_k\Phi_X^t(x/\varepsilon_k). Hence AkAC00\lVert A_k-A\rVert_{C^0}\to0, every coefficient is CC^\infty with all derivatives bounded for each fixed kk, and every integral in (3.26) is finite. If μk\mu_k is the pushforward of ν\nu by xεkxx\mapsto\varepsilon_kx, then μkδ0\mu_k\Rightarrow\delta_0 and hμk(Φk)=hν(ΦX)>0h_{\mu_k}(\Phi_k)=h_\nu(\Phi_X)>0, whereas the limiting zero flow has hδ0(Φ)=0h_{\delta_0}(\Phi)=0. All printed hypotheses hold, but the asserted inequality fails. A valid theorem needs substantially stronger, uniform smooth control than C0C^0 convergence alone.

Full paper, version 1
Theorems 4.2 and 4.4Not able to verify

The application statements are not independently established

Pages 16–18 · Theorems 4.2 and 4.4 · arXiv:2608.00370v1

These theorems add a uniform Lyapunov condition and nondegeneracy of the diffusion on the relevant set, so the deterministic rescaling counterexample to Theorem 3.7 does not directly apply. Their proofs, however, consist of invoking Theorem 3.7 after Proposition 4.1 or Lemma 4.3. Since Theorem 3.7 is false and no replacement argument exploiting the additional hypotheses is supplied, a nontrivial proof obligation remains: one must derive entropy control uniform in kk, rather than merely finiteness of every fixed system's smooth norms. No proof or counterexample for these narrower statements is supplied here.

02Proofs5 reported findingsContains incorrect or incomplete proofs

The proof of the main theorem cannot be repaired under its printed hypotheses because the theorem has an explicit counterexample. Two earlier arguments also contain independent substantive gaps: Lemma 3.3 uses a false entropy identity for a fixed partition, and Theorem 3.5 treats merely measurable Oseledets data as continuous on an arbitrary compact set and omits the zero-positive-exponent case. Two mechanical notation errors are reported separately in yellow.

Proof of Theorem 3.7Incorrect as written

The argument lacks the uniform smooth control excluded by the counterexample

Page 15 · Equations (3.27)–(3.29) · arXiv:2608.00370v1

Equation (3.29) makes the local-volume term vanish separately for each Φk\Phi_k by allowing the differentiability order rr to tend to infinity, but the hypotheses contain no bound uniform in kk on the higher derivatives or on the associated local complexity. The rescaled-flow construction in the statements finding satisfies (3.26) for every fixed kk while retaining positive entropy, so the asserted conclusion cannot follow. Repair classification: No repair under the stated hypotheses; the theorem must be strengthened by a uniform topology or explicit uniform tail-entropy estimate.

Lemma 3.3Incomplete as written

The proof uses a false fixed-partition entropy identity

Pages 6–8 · display following Equation (3.6) · arXiv:2608.00370v1

The proof writes hμ(Φ,α)=N1hμ(ΦN,α)h_\mu(\Phi,\alpha)=N^{-1}h_\mu(\Phi^N,\alpha) for the same fixed partition α\alpha. In general only the system entropy scales as hμ(ΦN)=Nhμ(Φ)h_\mu(\Phi^N)=Nh_\mu(\Phi); for a fixed partition the correct NN-block relation uses j=0N1Φjα\bigvee_{j=0}^{N-1}\Phi^{-j}\alpha. Substituting that block changes the conditional-partition argument and must be propagated through (3.1)–(3.6). Repair classification: Plausible repair only, by giving the standard local-entropy proof with the full NN-block partition; the manuscript does not do so.

Theorem 3.5Incomplete as written

The Lyapunov-chart construction omits measurable-selection and exponent cases

Pages 11–14 · proof of Theorem 3.5, especially Equations (3.20)–(3.21) · arXiv:2608.00370v1

The proof first infers from r(Φ,ϵ,Λ)>0r(\Phi,\epsilon,\Lambda)>0 that a positive Lyapunov exponent exists, which does not follow from Ruelle's inequality. It then asserts that the Oseledets bundles and the measurable chart-size and angle functions are continuous on the arbitrary compact set Λ\Lambda for almost every noise realization. Oseledets theory supplies measurability, while a Lusin argument gives continuity only after restricting to a suitably chosen large-measure compact subset and controlling varying multiplicities. Consequently the positive infima defining M2(ω)M_2(\omega) and the subsequent finite covering are not established in the claimed scope. Repair classification: No repair supplied; the missing exponent case and a correct Pesin-block selection must be incorporated throughout the volume comparison.

Definition of $r(\Phi,n,\delta,\epsilon,\Lambda,x,\omega)$Typo

The separated-pair formula repeats the base point

Page 6 · paragraph before Lemma 3.3 · arXiv:2608.00370v1

For distinct y,zFn(x,ω)y,z\in F_n(x,\omega), the printed separation condition compares Φi(x,ω)\Phi^i(x,\omega) with Φi(y,ω)\Phi^i(y,\omega). Replace x,yx,y in that comparison by y,zy,z. The surrounding phrase 'for any yzy\ne z' and every later use as an (n,δ)(n,\delta)-separated set determine this correction uniquely.

Definition of $\ln^+$Typo

The positive logarithm is printed as a positive part of its argument

Page 11 · definition immediately following Gloc\overline G_{\mathrm{loc}} · arXiv:2608.00370v1

The paper prints ln+x=max{1,x}\ln^+x=\max\{1,x\}. Replace this by ln+x=max{0,lnx}\ln^+x=\max\{0,\ln x\}. The notation, the logarithmic growth-rate formulas, and the integrability conditions determine the intended correction mechanically; leaving the printed definition literal would invalidate the stated growth normalization.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2608.00370v1
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Zhenxin Liu, Lixin Zhang
Audit date
August 18, 2026
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