arXiv:2405.17122v2

Relative stationary dynamical systems

Tattwamasi Amrutam, Martin Klötzer, Hanna Oppelmayer

math.DSmath.FA37A5022F1037B0560J50

Abstract

Let GG be a locally compact second countable group equipped with an admissible non-degenerate Borel probability measure μμ. We generalize the notion of μμ-stationary systems to μμ-stationary GG-factor maps π:(X,ν)(Y,η)π: (X,ν)\to (Y,η). For these stationary relations between dynamical systems, we provide a structure theorem, which generalizes the structure theorem of Furstenberg-Glasner. Furthermore, we show the existence and uniqueness of a relative version of the Poisson boundary in this setup.

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Audited against arXiv v2

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 unsupported statements

The relative structure theorem is supported, but the claimed maximal relative Poisson boundary is not fully established: the decisive quotient is taken under a transformation that is not measure preserving, without proving the required invariant-sigma-algebra identification and factorization.

Theorem 1.2 / Theorem 6.5Correct

Relative structure theorem

Pages 3 and 26–27 · Theorem 1.2 / Theorem 6.5 · arXiv:2405.17122v2

The boundary-limit measure, relative joining, and its two projections have the asserted relative proximality, relative measure-preservation, and limiting injectivity properties.

Theorem 1.1Not able to verify

Maximality of the proposed relative Poisson boundary is not established

Pages 2 and 28–30 · Theorem 1.1 and Proposition 7.1 · arXiv:2405.17122v2

The proof defines T(g1,g2,,y)=(g1g2,g3,,y)T(g_1,g_2,\ldots,y)=(g_1g_2,g_3,\ldots,y) on the product measure μNη\mu^{\mathbb{N}}\otimes\eta and then takes its ‘ergodic components’. In general TT sends the first-coordinate law μ\mu to μμ\mu*\mu, so it is not measure preserving and may not even preserve the measure class. The paper gives no theorem identifying the invariant sigma-algebra quotient of this nonsingular map with Poi(G,μ)Y\operatorname{Poi}(G,\mu)\otimes Y, nor a proof that the boundary map factors through that quotient. This is the step needed for maximality.

02Proofs2 reported findingsContains incorrect or incomplete proofs

Section 7 treats a non-measure-preserving coalescing map as though standard ergodic decomposition and quotient arguments applied automatically.

Section 7.1Incomplete as written

The coalescing map does not preserve the declared product measure

Page 28 · construction preceding Proposition 7.1 · arXiv:2405.17122v2

Under μN\mu^{\mathbb{N}}, the first coordinate of TωT\omega has law μμ\mu*\mu rather than μ\mu. Thus the sentence ‘we may take the TT-ergodic components’ is not justified by the usual probability-preserving ergodic decomposition. A repair would need a precise tail-boundary theorem for this coalescing map, including the induced GG-action and the product identification with YY; none is supplied.

Proposition 7.1Incomplete as written

The boundary map is assumed to descend to the unproved quotient

Pages 29–30 · proof of Proposition 7.1 · arXiv:2405.17122v2

The formula π([ω],y)=bnd(ω,y)\pi([\omega],y)=\operatorname{bnd}(\omega,y) is valid only after proving that bnd\operatorname{bnd} is measurable with respect to the quotient sigma-algebra and that the quotient carries the claimed Poisson-boundary measure. The proof cites only equivariance and measurability on the original path space, which do not establish this descent.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2405.17122v2
Authors listed
Tattwamasi Amrutam, Martin Klötzer, Hanna Oppelmayer
Audit date
August 18, 2026
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