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JOURNALS // Algebra and Discrete Mathematics // Archive

Algebra Discrete Math., 2020 Volume 30, Issue 1, Pages 97–117 (Mi adm768)

RESEARCH ARTICLE

On growth of generalized Grigorchuk's overgroups

S. T. Samarakoon

Department of Mathematics, Mailstop 3368, Texas A&M University, College Station, TX 77843-3368, United States

Abstract: Grigorchuk's Overgroup $\widetilde{\mathcal{G}}$, is a branch group of intermediate growth. It contains the first Grigorchuk's torsion group $\mathcal{G}$ of intermediate growth constructed in 1980, but also has elements of infinite order. Its growth is substantially greater than the growth of $\mathcal{G}$. The group $\mathcal{G}$, corresponding to the sequence $(012)^\infty = 012012 \cdots$, is a member of the family $\{ G_\omega | \omega \in \Omega = \{ 0, 1, 2 \}^\mathbb{N} \}$ consisting of groups of intermediate growth when sequence $\omega$ is not eventually constant. Following this construction, we define the family $\{ \widetilde{G}_\omega, \omega \in \Omega \}$ of generalized overgroups. Then $\widetilde{\mathcal{G}} = \widetilde{G}_{(012)^\infty}$ and $G_\omega$ is a subgroup of $\widetilde{G}_\omega$ for each $\omega \in \Omega$. We prove, if $\omega$ is eventually constant, then $\widetilde{G}_\omega$ is of polynomial growth and if $\omega$ is not eventually constant, then $\widetilde{G}_\omega$ is of intermediate growth.

Keywords: growth of groups, intermediate growth, Grigorchuk group, growth bounds.

MSC: 20E08

Received: 06.09.2019
Revised: 30.06.2020

Language: English

DOI: 10.12958/adm1451



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