The level four braid group
Geometric Topology
2021-04-23 v3
Abstract
By evaluating the Burau representation at t=-1, we obtain a symplectic representation of the braid group. We define the congruence subgroups of the braid group to be the preimages of the principal congruence subgroups of the symplectic group. Our main result is that the level four congruence subgroup of the braid group is equal to the group generated by squares of Dehn twists and is also equal to the group generated by squares of pure braids. We also compute the image of the point pushing subgroup under the symplectic representation.
Keywords
Cite
@article{arxiv.1410.7416,
title = {The level four braid group},
author = {Tara E. Brendle and Dan Margalit},
journal= {arXiv preprint arXiv:1410.7416},
year = {2021}
}
Comments
17 pages, 4 figures, with corrections to the published version; erratum to the published version attached