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2507.12736

Finitude of physical measures for Markovian random maps

Pablo G. Barrientos, Dominique Malicet, Fumihiko Nakamura, Yushi Nakano, Hisayoshi Toyokawa

correctmedium confidence
Category
Not specified
Journal tier
Strong Field
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper proves Theorem E by reducing the Markov-driven system to an i.i.d. representation h, showing h is Lipschitz with an exponential moment, applying a Bernoulli (i.i.d.) mostly-contracting result to obtain quasi-compactness of the annealed Koopman operator, and then transferring both quasi-compactness and (fpm) back to the original Markov setting via the conjugacy π and the characterization of P-Markovian invariant measures (notably Theorem 3.2 and the basin-transfer lemmas) . By contrast, the candidate solution hinges on deducing Λ=∑t π(t)log Lip(ft)<0 from the assumption λ(f)<0 (sup over P-Markovian invariant measures of maximal Lyapunov exponents), and then perturbing ρ(Q Dα). But λ(f)<0 only implies λ(μ̄)≤Λ for every P‑Markovian μ̄; it does not force Λ<0. Hence the key spectral step ρ(Q Dα)<1 is unjustified under the paper’s hypotheses. The candidate further asserts uniqueness of a physical measure (r=1) via a contraction in a Hölder dual metric, which is strictly stronger than (and not implied by) the paper’s (fpm) conclusion of finiteness; the paper never claims uniqueness, and in general only finiteness can be guaranteed .

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} strong field

\textbf{Justification:}

The paper cleanly transports finiteness-of-physical-measures and quasi-compactness results from i.i.d. to Markov noise via an i.i.d. representation and a well-constructed conjugacy. The main theorems are stated precisely, hypotheses are appropriate (finite state space, mostly contracting), and the reductions to established Bernoulli results are legitimate. Minor clarifications to guide the reader through the transfer steps and to flag the precise points where prior results are invoked would improve accessibility.