On the Hausdorff dimension and attracting laminations for fully irreducible automorphisms of free groups

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Auteur principal: Kapovich, Ilya
Format: Preprint
Publié: 2024
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author Kapovich, Ilya
author_facet Kapovich, Ilya
contents Motivated by a classic theorem of Birman and Series about the set of complete simple geodesics on a hyperbolic surface, we study the Hausdorff dimension of the set of endpoints in $\partial F_r$ of some abstract algebraic laminations associated with free group automorphisms. For an exponentially growing outer automorphism $ϕ\in Out(F_r)$ we show that the set of endpoints $\mathcal E_{L}\subseteq \partial F_r$ of any of the \emph{attracting laminations} $L$ of $ϕ$ has Hausdorff dimension $0$ for any tree $T\in cv_r$ and any visual metric on the boundary $\partial T=\partial F_r$. If $ϕ\in Out(F_r)$ is an atoroidal and fully irreducible, we deduce the same conclusion for the set of endpoints of the ending lamination $Λ_ϕ$ of $ϕ$ that gets collapsed by the Cannon-Thurston map $\partial F_r\to \partial G_ϕ$ for the associated free-by-cyclic group $G_ϕ=F_r\rtimes_ϕ\mathbb Z$.
format Preprint
id arxiv_https___arxiv_org_abs_2410_02058
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle On the Hausdorff dimension and attracting laminations for fully irreducible automorphisms of free groups
Kapovich, Ilya
Group Theory
Dynamical Systems
Geometric Topology
Primary 20F65, Secondary 20F10, 20F67, 37B10, 37D99, 57M99
Motivated by a classic theorem of Birman and Series about the set of complete simple geodesics on a hyperbolic surface, we study the Hausdorff dimension of the set of endpoints in $\partial F_r$ of some abstract algebraic laminations associated with free group automorphisms. For an exponentially growing outer automorphism $ϕ\in Out(F_r)$ we show that the set of endpoints $\mathcal E_{L}\subseteq \partial F_r$ of any of the \emph{attracting laminations} $L$ of $ϕ$ has Hausdorff dimension $0$ for any tree $T\in cv_r$ and any visual metric on the boundary $\partial T=\partial F_r$. If $ϕ\in Out(F_r)$ is an atoroidal and fully irreducible, we deduce the same conclusion for the set of endpoints of the ending lamination $Λ_ϕ$ of $ϕ$ that gets collapsed by the Cannon-Thurston map $\partial F_r\to \partial G_ϕ$ for the associated free-by-cyclic group $G_ϕ=F_r\rtimes_ϕ\mathbb Z$.
title On the Hausdorff dimension and attracting laminations for fully irreducible automorphisms of free groups
topic Group Theory
Dynamical Systems
Geometric Topology
Primary 20F65, Secondary 20F10, 20F67, 37B10, 37D99, 57M99
url https://arxiv.org/abs/2410.02058