Automorphism groups of random substitution subshifts

Fokkink, Robbert; Rust, Dan and Salo, Ville (2024). Automorphism groups of random substitution subshifts. Indagationes Mathematicae, 35(5) pp. 931–958.

DOI: https://doi.org/10.1016/j.indag.2023.08.006

Abstract

We prove that for a suitably nice class of random substitutions, their corresponding subshifts have automorphism groups that contain an infinite simple subgroup and a copy of the automorphism group of a full shift. Hence, they are countable, non-amenable and non-residually finite. To show this, we introduce the concept of shuffles and generalised shuffles for random substitutions, as well as a local version of recognisability for random substitutions that will be of independent interest. Without recognisability, we need a more refined notion of recognisable words in order to understand their automorphisms. We show that the existence of a single recognisable word is often enough to embed the automorphism group of a full shift in the automorphism group of the random substitution subshift.

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