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Anna Erschler
Critical constants for recurrence of random walks on $G$-spaces
(Constantes critiques pour la récurrence des marches aléatoires sur les $G$-espace.)
Annales de l'institut Fourier, 55 no. 2 (2005), p. 493-509, doi: 10.5802/aif.2105
Article PDF | Reviews MR 2147898 | Zbl 02171516 | 1 citation in Cedram
Class. Math.: 20F65, 20E08, 60B15
Keywords: growth of groups, Grigorchuk groups, branch groups, random walks, recurrence, drift

Résumé - Abstract

We introduce the notion of a critical constant $c_{rt}$ for recurrence of random walks on $G$-spaces. For a subgroup $H$ of a finitely generated group $G$ the critical constant is an asymptotic invariant of the quotient $G$-space $G/H$. We show that for any infinite $G$-space $c_{rt} \ge 1/2$. We say that $G/H$ is very small if $c_{rt}<1$. For a normal subgroup $H$ the quotient space $G/H$ is very small if and only if it is finite. However, we give examples of infinite very small $G$-spaces. We show also that critical constants for recurrence can be used to estimate the growth of groups as well as the drift for random walks on groups.

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