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We prove that if G_P is a finitely constrained group of binary rooted tree automorphisms (a group binary tree subshift of finite type) defined by an essential pattern group P of pattern size d, d>1, and if G_P has maximal Hausdorff…

Group Theory · Mathematics 2015-12-30 Andrew Penland , Zoran Sunic

This work continues the study of the properties of finitely constrained groups of binary tree automorphisms in terms of their Hausdorff dimension. We prove that there are exactly $2^{2d-3}$ finitely constrained groups of binary tree…

Group Theory · Mathematics 2017-10-17 Andrew Penland

Firstly, we completely determine the self-similar Hausdorff spectrum of the group of $q$-adic automorphisms where $q$ is a prime power, answering a question of Grigorchuk. Indeed, we take a further step and completely determine its…

Group Theory · Mathematics 2026-01-29 Jorge Fariña-Asategui

We show that the Hausdorff dimension of the closure of the second Grigorchuk group is 43/128. Furthermore we establish that the second Grigorchuk group is super strongly fractal and that its automorphism group equals its normaliser in the…

Group Theory · Mathematics 2020-07-20 Marialaura Noce , Anitha Thillaisundaram

Let $G$ be a finitely generated pro-$p$ group, equipped with the $p$-power series. The associated metric and Hausdorff dimension function give rise to the Hausdorff spectrum, which consists of the Hausdorff dimensions of closed subgroups of…

Group Theory · Mathematics 2019-02-26 Benjamin Klopsch , Anitha Thillaisundaram , Amaia Zugadi-Reizabal

An explicit algorithm is given for the computation of the Hausdorff dimension of the closure of a regular branch group in terms of an arbitrary branch structure. We implement this algorithm in GAP and apply it to a family of GGS-groups…

Group Theory · Mathematics 2026-01-29 Jorge Fariña-Asategui

Let $G$ be a finitely generated pro-$p$ group of positive rank gradient. Motivated by the study of Hausdorff dimension, we show that finitely generated closed subgroups $H$ of infinite index in $G$ never contain any infinite subgroups $K$…

Group Theory · Mathematics 2024-08-28 Oihana Garaialde Ocaña , Alejandra Garrido , Benjamin Klopsch

We answer two longstanding questions of Klopsch (1999) and Shalev (2000) by proving that the finitely generated Hausdorff spectrum of the closure of a finitely generated regular branch group with respect to the level-stabilizer filtration…

Group Theory · Mathematics 2025-04-17 Jorge Fariña-Asategui , Oihana Garaialde Ocaña , Jone Uria-Albizuri

Based on the work of Abercrombie, Barnea and Shalev gave an explicit formula for the Hausdorff dimension of a group acting on a rooted tree. We focus here on the binary tree T. Abert and Virag showed that there exist finitely generated (but…

Group Theory · Mathematics 2008-09-05 Olivier Siegenthaler

A countably based profinite group can be naturally seen as a metric space with respect to a given filtration, and thus, it has a well defined Hausdorff dimension function. Barnea and Shalev found a group theoretical expression for the…

Group Theory · Mathematics 2021-01-26 Iker de las Heras

Groups of finite type (also called finitely constrained groups), introduced by Grigorchuk, are known to be the closure of regular branch groups. This article explores many of their properties. Firstly, we prove that being finitely…

Group Theory · Mathematics 2025-09-05 Santiago Radi

We compute the Hausdorff dimension of the closure of the generalized Brunner-Sidki-Vieira group acting on the $m$-adic tree for $m\ge 2$, providing the first examples of self-similar topologically finitely generated closed subgroups of…

Group Theory · Mathematics 2024-03-26 Jorge Fariña-Asategui , Mikel E. Garciarena

We study the finitely generated Hausdorff spectrum of spinal automorphism groups acting on rooted trees. Given any $\alpha \in [0,1]$, we construct a branch group $G_\alpha$ such that $G_\alpha$ has a finitely generated subgroup $H$ where…

Group Theory · Mathematics 2013-01-30 Elisabeth Fink

We study the Hausdorff and the box dimensions of closed invariant subsets of the space of pointed trees, equipped with a pseudogroup action. This pseudogroup dynamical system can be regarded as a generalization of a shift space. We show…

Dynamical Systems · Mathematics 2021-12-22 Olga Lukina

This thesis has three goals related to the automorphism groups of finite $p$-groups. The primary goal is to provide a complete proof of a theorem showing that, in some asymptotic sense, the automorphism group of almost every finite…

Group Theory · Mathematics 2007-11-20 Geir T. Helleloid

Ab\'ert and Vir\'ag proved in 2005 that the Hausdorff dimension of a non-trivial normal subgroup of a level-transitive 1-dimensional subgroup of the group of $p$-adic automorphisms $W_p$ is always 1. They further asked whether the same…

Group Theory · Mathematics 2025-05-30 Jorge Fariña-Asategui

In this article we prove that the arithmetic profinite iterated monodromy group of a post-critically infinite unicritical polynomial is regular branch (and so of positive Hausdorff dimension), and has positive fixed-point proportion when…

Group Theory · Mathematics 2026-02-26 Santiago Radi

A non-trivial finitely generated pro-$p$ group $G$ is said to be strongly hereditarily self-similar of index $p$ if every non-trivial finitely generated closed subgroup of $G$ admits a faithful self-similar action on a $p$-ary tree. We…

Group Theory · Mathematics 2020-02-07 Francesco Noseda , Ilir Snopce

We give upper and lower bounds for the Hausdorff dimensions for a class of graph-directed measures when its underlying directed graph is the infinite N-ary tree. These measures are different from graph-directed self-similar measures driven…

Classical Analysis and ODEs · Mathematics 2020-04-28 Kazuki Okamura

We disprove a well-known conjecture of Boston (2000), which claims that a just-infinite pro-$p$ group is branch if and only if it admits a positive-dimensional embedding in the group of $p$-adic automorphisms. This is obtained as a result…

Group Theory · Mathematics 2025-07-31 Jorge Fariña-Asategui
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