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2201.00737

Counting and boundary limit theorems for representations of Gromov-hyperbolic groups

Stephen Cantrell, Cagri Sert

correctmedium confidence
Category
Not specified
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:56 AM

Audit review

The paper proves exponential large deviations for log‖ρ(g)‖ under uniform counting on spheres in non‑elementary hyperbolic groups (Theorem 1.6), via a boundary approach: first establish an almost-sure large deviation theorem for Patterson–Sullivan typical geodesic rays (Theorem 1.10), then transfer to counting; it also develops the Markov coding and Parry-like measures in detail and handles periodicity and multiple maximal components (Sections 2, 3, 6, 8) . The candidate’s solution proves the same counting large deviations by directly comparing uniform counting on length‑n geodesics with the Parry (maximal entropy) Markov law on the Cannon/shortlex automaton, and then invoking Bougerol’s large deviations for Markovian matrix products; this is a method explicitly noted as viable in Remark 6.3 (though not pursued there) . The model’s sketch omits technicalities that the paper handles carefully (non‑irreducibility and periodicity of the automaton; uniform Doeblin/minorization; handling operator vs vector norms), but these are standard fixable details (e.g., passing to a p‑step skeleton and decomposing across maximal components) and do not alter correctness. Hence both are correct, but the proofs are different in emphasis.

Referee report (LaTeX)

\textbf{Recommendation:} major revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The paper’s result matches the problem and is proved with full technical care, leveraging boundary methods and Markovian matrix product theory. The candidate solution follows a different but standard route (Parry measure + Bougerol LDP) that the paper notes is viable; however, it omits key reductions (periodicity, component decomposition, minorization) and the operator-norm vs vector-cocycle point. These are fixable but should be made explicit for a complete proof.