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
- arXiv Links
- Abstract ↗PDF ↗
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.