Subshifts and colorings on ascending HNN-extensions of finitely generated abelian groups

Abstract

For an ascending HNN-extension $G{\ast }_{\psi }$ of a finitely generated abelian group $G$, we study how a synchronization between the geometry of the group and weak periodicity of a configuration in ${\mathcal{A}}^{G{\ast }_{\psi }}$ forces global constraints on it, as well as in subshifts containing it. A particular case are Baumslag-Solitar groups $\mathrm{BS}(1,N)$, $N\ge 2$, for which our results imply that a $\mathrm{BS}(1,N)$-SFT which contains a configuration with period $a^{N^{\ell }}$, $\ell \ge 0$, must contain a strongly periodic configuration with monochromatic $\mathbb{Z}$-sections. Then we study proper $n$-colorings, $n\ge 3$, of the (right) Cayley graph of $\mathrm{BS}(1,N)$, estimating the entropy of the associated subshift together with its mixing properties. We prove that $\mathrm{BS}(1,N)$ admits a frozen $n$-coloring if and only if $n=3$. We finally suggest generalizations of the latter results to $n$-colorings of ascending HNN-extensions of finitely generated abelian groups.

22 pages

References in corpus (2)

• Proper 3-colorings of ${\mathbb{Z}}^2$ are Bernoulli
• Weakly and Strongly Aperiodic Subshifts of Finite Type on Baumslag-Solitar Groups