Beta-expansions, natural extensions and multiple tilings associated with Pisot units

Charlene Kalle (1) , Wolfgang Steiner (2)

1 Department of Mathematics
2 LIAFA - Laboratoire d'informatique Algorithmique : Fondements et Applications

From the works of Rauzy and Thurston, we know how to construct (multiple) tilings of some Euclidean space using the conjugates of a Pisot unit $\beta$ and the greedy $\beta$-transformation. In this paper, we consider different transformations generating expansions in base~$\beta$, including cases where the associated subshift is not sofic. Under certain mild conditions, we show that they give multiple tilings. We also give a necessary and sufficient condition for the tiling property, generalizing the weak finiteness property (W) for greedy $\beta$-expansions. Remarkably, the symmetric $\beta$-transformation does not satisfy this condition when $\beta$ is the smallest Pisot number or the Tribonacci number. This means that the Pisot conjecture on tilings cannot be extended to the symmetric $\beta$-transformation. Closely related to these (multiple) tilings are natural extensions of the transformations, which have many nice properties: they are invariant under the Lebesgue measure; under certain conditions, they provide Markov partitions of the torus; they characterize the numbers with purely periodic expansion, and they allow determining any digit in an expansion without knowing the other digits.

Domaines: Systèmes dynamiques [math.DS]; Théorie des nombres [math.NT]

Charlene Kalle, Wolfgang Steiner. Beta-expansions, natural extensions and multiple tilings associated with Pisot units. Transactions of the American Mathematical Society, 2012, 364 (5), pp.2281-2318. ⟨10.1090/S0002-9947-2012-05362-1⟩. ⟨hal-00404226v3⟩