Perfect models for finite Coxeter groups

TL;DR

This paper classifies which finite Coxeter groups possess perfect models, revealing that only specific types do, and explores their properties and implications for group representations.

Contribution

It provides a complete classification of finite Coxeter groups with perfect models and analyzes their uniqueness and representation-theoretic properties.

Findings

Types A_n, B_n, D_{2n+1}, H_3, and I_2(n) have perfect models.

Most groups outside A_3, B_n, and H_3 have at most one perfect model.

Induction from certain parabolic subgroups is never multiplicity-free.

Abstract

A model for a finite group is a set of linear characters of subgroups that can be induced to obtain every irreducible character exactly once. A perfect model for a finite Coxeter group is a model in which the relevant subgroups are the quasiparabolic centralizers of perfect involutions. In prior work, we showed that perfect models give rise to interesting examples of $W$-graphs. Here, we classify which finite Coxeter groups have perfect models. Specifically, we prove that the irreducible finite Coxeter groups with perfect models are those of types $\mathsf{A}_{n}$, $\mathsf{B}_n$, $\mathsf{D}_{2n+1}$, $\mathsf{H}_3$, or $\mathsf{I}_2(n)$. We also show that up to a natural form of equivalence, outside types $\mathsf{A}_3$, $\mathsf{B}_n$, and $\mathsf{H}_3$, each irreducible finite Coxeter group has at most one perfect model. Along the way, we also prove a technical result about representations of finite Coxeter groups, namely, that induction from standard parabolic subgroups of corank at least two is never multiplicity-free.