English

Geometric generators for braid-like groups

Geometric Topology 2016-05-04 v2

Abstract

We study the problem of finding generators for the fundamental group G of a space of the following sort: one removes a family of complex hyperplanes from n dimensional complex vector space, or n dimensional complex hyperbolic space, or the Hermitian symmetric space for O(2,n), and then takes the quotient by a discrete group PΓP{\Gamma}. The classical example is the braid group, but there are many similar "braid-like" groups that arise in topology and algebraic geometry. Our main result is that if PΓP{\Gamma} contains reflections in the hyperplanes nearest the basepoint, and these reflections satisfy a certain property, then G is generated by the analogues of the generators of the classical braid group. We apply this to obtain generators for G in a particular intricate example in complex hyperbolic space of dimension 13. The interest in this example comes from a conjectured relationship between this braid-like group and the monster simple group M, that gives geometric meaning to the generators and relations in the Conway-Simons presentation of (M×M):2(M \times M):2.

Keywords

Cite

@article{arxiv.1403.2401,
  title  = {Geometric generators for braid-like groups},
  author = {Daniel Allcock and Tathagata Basak},
  journal= {arXiv preprint arXiv:1403.2401},
  year   = {2016}
}

Comments

24 pages, 5 figures. Revised version 2: minor typos corrected, expository material added, bibliography updated

R2 v1 2026-06-22T03:23:53.715Z