Subgroup tameness conjecture for hyperbolic mapping tori of free groups

From papers

Let F\mathbb{F} be a finitely generated free group and let ψF\psi\to \mathbb{F} be a fully irreducible monomorphism, meaning that no proper nontrivial finitely generated free factor is mapped into a conjugate of itself by a positive power of ψ\psi. Set G=M(ψ)G=M(\psi) and assume that GG is hyperbolic. For a finitely generated subgroup HGH\leqslant G, a fibre subgroup is one arising from an automorphism of a finite-index mapping-torus subgroup, and a semi-fibre subgroup is the analogous subgroup arising from a proper monomorphism. Subgroup tameness conjecture. Either HH is a fibre or semi-fibre subgroup of a finite-index subgroup of GG, or HH is quasi-convex. This is the proposed analogue of the subgroup tameness theorem for hyperbolic 3-manifold groups; the source attributes it to an AIM workshop and Abdenbi–Wise, and gives no resolution.

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Sources & referencesView supporting material

Primary source

Marco Linton, “The geometry of subgroups of mapping tori of free groups”, arXiv:2510.03145 (2025).

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