Parametrized braid groups of Chevalley groups.

Abstract

We introduce the notion of a braid group parametrized by a ring, which is defined by generators and relations and based on the geometric idea of painted braids. We show that the parametrized braid group is isomorphic to the semi-direct product of the Steinberg group (of the ring) with the classical braid group. The technical heart of the proof is the Pure Braid Lemma, which asserts that certain elements of the parametrized braid group commute with the pure braid group. This first part treats the case of the root system An; in the second part we prove a similar theorem for the root system Dn. 2000 Mathematics Subject Classification: Primary 20F36; Secondary 19Cxx; 20F55. Keywords and Phrases: Braid group, Steinberg group, parametrized braid group, root system.