A Contracting Fractal Group, Schreier Graphs and The Spectra

Abstract

This paper explores a previously uncharted automaton group generated by a 5-state automaton $(\Pi ,A)$ acts by self-similarity on the regular rooted tree $A^{\ast }$ over a 2-letter alphabet set $A$. Group $G$ has been subjected to several observations that reveal the self-similar $G$-action possesses several notable characteristics: it is a weak branch, contracting, fractal group, and satisfies the open set condition with an exponential growth rate in activity. The corresponding Schreier graphs $\Gamma$ of the group action on the binary rooted tree, for $n\le 12$, are presented. Furthermore, we delve into a numerical approximation of the spectrum of the discrete Laplacian operator, which is defined on the limit Schreier graph $\hat{\Gamma }={\lim }_{n\to \infty }{\Gamma }_n$.