On the Burau representation of $B_3$

Vasudha Bharathram, Joan Birman

Published 2022-08-25Version 1

We study the Burau representation of the braid group $B_n$ in the case where $n=3$. We give three novel topological proofs that the Burau representation of $B_3$ is faithful, and a proof that it's faithful modulo $p$ for all integers $p>1$. We then classify conjugacy classes in the image of the Burau representation in $\text{GL}(2, \mathbb{Z}[t, t^{-1}])$ in a way that takes account of the fact that braids are geometrically oriented, and use that fact to give a new, linear time solution to the conjugacy problem in $B_3$. We pose several open problems about $B_n$.