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3. Grigorchuk’s group, branch groups and groups of intermediate growth


    1. Add remark

      Problem 3.1.

      Is there a f.p. branch group? Is there a f.p. amenable branch group?

        •     Def: A subgroup $H$ of a group $G$ is commensurated if $\forall g \in G$, $g^{-1}Hg \cap H$ has finite index in $H$.

          Thm(Wesolek): A finitely generated branch group is just infinite if and only if every commensurated subgroup is either finite or of finite index.

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          Problem 3.2.

          Find a combinatorial proof of the following: every commensurated subgroup of a finitely generated branch group is either finite or of finite index.
              The problem is interesting even in the special case of Grigorchuk’s group $G$


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              Problem 3.3.

              Is the universal Grigorchuk group amenable?
                1. Remark. If this group is amenable, then the Folner function of this group is universal bound on Folner function of $G_\omega$


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                      Problem 3.4.

                      Find bounds on Folner functions for the Grigorchuk group $G$.


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                          Problem 3.5.

                          Is the sequence of balls $B_n(e)$ in Grigorchuk’s group $G$ a Folner sequence?


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                              Problem 3.6.

                              Does the limit \[ \lim_{n\rightarrow\infty} \frac{\log \log (B_G(n))}{\log n} \] exist for the Grigorchuk group?


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                                  Problem 3.7.

                                  Is $\rho_c<1$ for all groups of intermediate growth?


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                                      Problem 3.8.

                                      Is there a finitely presented amenable group that surjects onto a group of intermediate growth?


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                                          Problem 3.9.

                                          Are polynomial activity automata groups amenable?

                                              Cite this as: AimPL: Amenability of discrete groups, available at http://aimpl.org/amenablediscrete.