Burau representation of braid groups and $q$-rationals

Abstract

We establish a link between the new theory of $q$-deformed rational numbers and the classical Burau representation of the braid group ${\mathrm{B}}_3$. We apply this link to the open problem of classification of faithful complex specializations of this representation. As a result we provide an answer to this problem in terms of the singular set of the $q$-rationals and prove the faithfulness of the Burau representation specialized at complex $t\in {\mathbb{C}}^{\ast }$ outside the annulus $3-2\sqrt{2}\le |t|\le 3+2\sqrt{2}.$