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The reflective Lorentzian lattices of rank 3

About this Title

Daniel Allcock, Department of Mathematics, U.T. Austin

Publication: Memoirs of the American Mathematical Society
Publication Year: 2012; Volume 220, Number 1033
ISBNs: 978-0-8218-6911-6 (print); 978-0-8218-9203-9 (online)
DOI: https://doi.org/10.1090/S0065-9266-2012-00648-4
Published electronically: March 1, 2012
Keywords: Lorentzian lattice, Weyl group, Coxeter group, Vinberg’s algorithm
MSC: Primary 11H56; Secondary 20F55, 22E40

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Table of Contents

Chapters

  • Introduction
  • 1. Background
  • 2. The Classification Theorem
  • 3. The Reflective Lattices

Abstract

We classify all the symmetric integer bilinear forms of signature $(2,1)$ whose isometry groups are generated up to finite index by reflections. There are 8,595 of them up to scale, whose 374 distinct Weyl groups fall into 39 commensurability classes. This extends Nikulin’s enumeration of the strongly square-free cases. Our technique is an analysis of the shape of the Weyl chamber, followed by computer work using Vinberg’s algorithm and a “method of bijections”. We also correct a minor error in Conway and Sloane’s definition of their canonical $2$-adic symbol.

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