Balance properties of the fixed point of the substitutionassociated to quadratic simple Pisot numbers

Abstract

In this paper we will deal with the balance properties of the infinite binary words associated to β-integers when β is a quadratic simple Pisot number. Those words are the fixed points of the morphisms of the type $\varphi(A)=A^pB$, $\varphi(B)=A^q$ for $p\in\mathbb N$, $q\in\mathbb N$, $p\geq q$, where $\beta=\frac{p+\sqrt{p^2+4q}}{2}$. We will prove that such word is t-balanced with $t=1+\left[(p-1)/(p+1-q)\right]$. Finally, in the case that p < q it is known [B. Adamczewski, Theoret. Comput. Sci.273 (2002) 197–224] that the fixed point of the substitution $\varphi(A)=A^pB$, $\varphi(B)=A^q$ is not m-balanced for any m. We exhibit an infinite sequence of pairs of words with the unbalance property.