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On Growth of Generalized Grigorchuk's Overgroups

Group Theory 2019-09-05 v2

Abstract

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

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Cite

@article{arxiv.1909.01272,
  title  = {On Growth of Generalized Grigorchuk's Overgroups},
  author = {Supun T. Samarakoon},
  journal= {arXiv preprint arXiv:1909.01272},
  year   = {2019}
}

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