Strong boundedness of ${\rm SL}_2(R)$ for rings of S-algebraic integers with infinitely many units

Abstract

A group is called strongly bounded, if the speed with which it is generated by finitely many conjugacy classes has a positive, lower bound only dependent on the number of the conjugacy classes in question rather than the actual conjugacy classes. Earlier papers by Kedra, Libman and Martin and myself have shown that this is a property common to split Chevalley groups defined using an irreducible root system of rank at least $2$ and the ring of all S-algebraic integers and that the situation is dependent on the number theory of $R$ for ${\rm Sp}_4$ and $G_2.$ In this paper, we will show that ${\rm SL}_2(R)$ is also strongly bounded for $R$ the ring of all S-algebraic integers in a number field $K$ with $R$ having infinitely many units and will give a complete account of the existence of small conjugacy classes generating ${\rm SL}_2(R)$ in terms of the prime factorization of the rational primes $2$ and $3$ in $R.$