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2112.04458

Finitely generated simple left orderable groups with vanishing second bounded cohomology

Francesco Fournier-Facio, Yash Lodha

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

Audit review

The uploaded paper proves Theorem 1.2: for every quasi-periodic labelling ρ, H^2_b(G_ρ; R)=0, via a concrete argument using homogeneous cocycles, central extensions, and carefully constructed 2-boundedly acyclic subgroups with global fixpoints, culminating in Proposition 5.1 and the proof of Theorem 1.2 . By contrast, the candidate solution relies on an unsubstantiated “commuting-conjugates” criterion and an overgeneral low-degree dictionary equating vanishing H^2_b with absence of homogeneous quasimorphisms; this conflates distinct phenomena (the paper itself notes that injectivity of H^2_b→H^2 from the absence of quasimorphisms does not force H^2_b=0) . The model also misattributes the main vanishing theorem to a different preprint. Hence: paper correct; model’s proof sketch is not reliable.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} strong field

\textbf{Justification:}

The paper delivers a clear, correct solution to a concrete, recognized question about left orderable groups and second bounded cohomology. The proof is technically solid and conceptually tidy, relying on homogeneous cocycles and a well-designed use of 2-boundedly acyclic subgroups and support control. With a few small clarifications and signposting enhancements, the exposition would be excellent.