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arXiv · 2603.12095

Profinite isomorphisms, stable commutator length, and fixed point properties

Francesco Fournier-Facio
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Abstract

We construct Grothendieck pairs witnessing that the following are not profinite invariants: stable commutator length, quasimorphisms (answering a question of Echtler and Kammeyer), property NL (which obstructs actions on hyperbolic spaces), and property FW$_\infty$ (which obstructs actions on finite-dimensional CAT(0) cube complexes). We also recover that property FA and non-abelian free subgroups are not profinite invariants. The method combines Rips constructions with iterated group-theoretic Dehn filling on hyperbolic virtually special groups.

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Francesco Fournier-Facio. 2026-03-12. Profinite isomorphisms, stable commutator length, and fixed point properties. https://arxiv.org/abs/2603.12095

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