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The Weyl group of a root system is a subgroup generated by reflections through the hyperplanes orthogonal to the roots.
17
votes
Polynomial invariants of the exceptional Weyl groups
Keeping in mind that a generating set of invariant polynomials having the required degrees is not unique, various computations have been recorded in the literature. Those I was aware of before 1990 …
16
votes
Accepted
About the intrinsic definition of the Weyl group of complex semisimple Lie algebras
Probably the earliest intrinsic definition of Weyl group occurs in section 1.2 of the groundbreaking paper "Representations of Reductive Groups Over Finite Fields" by Deligne and Lusztig (Ann. of Math …
16
votes
Longest element of Weyl groups
EDIT: This is a belated attempt (motivated by a question from
Yongjun Xu) to answer the question more precisely than I did at first, with more emphasis on careful choice of a Coxeter element when the …
12
votes
0
answers
416
views
Reference for class of involutions containing longest element of finite Coxeter group?
Consider a finite (say irreducible) Coxeter group $W$ with a fixed generator set $S$ and rank $n$. This is the same thing as a finite real reflection group, generated by a set of “simple” reflectio …
11
votes
Accepted
Does -I belong to Weyl group?
As Koen S points out, the longest element of an irreducible Weyl group is treated in an earlier question (in fact, it comes up in several questions). The question asked here presupposes a standard li …
9
votes
2
answers
687
views
Reference for embeddings of reflection groups (related to folding ADE Coxeter graphs)?
There are a couple of indirect methods, using Lie theory or Springer's general theory of regular elements in (real, complex) reflection groups, to construct natural embeddings among certain Weyl group …
8
votes
Longest element of a Weyl group
The role of the longest element in $W$ emerges only gradually in the Chevalley structure theory. This is developed similarly but in slightly different styles in the three books with the same title Li …
8
votes
Cells in affine Weyl groups
You are asking a number of related questions here, most of which require more reading of Lusztig's papers. See the reference list in my conference paper here, for example. But note first that the n …
7
votes
Weyl groups of $E_6$ and $E_7$
It's important to emphasize that the simple group here is typically isomorphic to the rotation subgroup of $W$, which has index 2 and doesn't contain the reflections. So you need to look at the prec …
7
votes
1
answer
470
views
Centralizer of longest element in a finite irreducible Weyl group: related to folding of ADE...
Say $(W,S)$ is a finite Coxeter group, such as a Weyl group (which satisfies an additional crystallographic condition). Assume also that $W$ is irreducible. Then it has a longest element $w_o$ r …
6
votes
3
answers
977
views
Occurrences of a simple reflection in the longest element of a Weyl group?
While looking at a preprint I've just bumped into a question about the longest element $w_0$ of a Weyl group $W$ (say irreducible of a Lie type $A$ - $G$ and of rank $n>1$, to simplify). Suppose t …
5
votes
Conjugacy of Regular Semisimple Subalgebras
It would help to recall Dynkin's definition of "regular semisimple subalgebra" of a complex semisimple Lie algebra (say $\mathfrak{g}$), which has not become standard in later literature. This just …
4
votes
Weyl group elements fixing a set of simple roots
I'm not sure whether there is an efficient way to answer your question (or a written reference), but it's possible to analyze the situation case-by-case.
It's probably best to start with an irreducib …
4
votes
Reference for embeddings of reflection groups (related to folding ADE Coxeter graphs)?
Rather than overload the question with side remarks, I'll add some background here in community-wiki format to indicate what can be gotten from Springer's relatively elementary treatment of regular el …
4
votes
Diagonal automorphisms for twisted Chevalley groups
First of all, I'd inquire what role the characteristic of the field plays here. It's true that the finite twisted groups rely on characteristics 2, 3 especiallu, but infinite twisted groups include …