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This tag is used if a reference is needed in a paper or textbook on a specific result.

5 votes
Accepted

History of the study of Verma modules in terms of Kazhdan Lusztig Theory

It's probably too soon to expect a good historical overview, but for example Steve Kleiman has already written a scholarly article (The development of intersection homology theory) emphasizing the ori …
Jim Humphreys's user avatar
1 vote

Weight spaces of representations of finite dimensional simple Lie algebras

EDIT: I misunderstood at first what your basic question is but now understand it better. One cautionary case comes from older work of Richard Block here, which includes the rank 1 simple Lie algeb …
Jim Humphreys's user avatar
7 votes
Accepted

For $G$ an adjoint Chevalley group, are all of $G(\mathbb Z)$'s finite-index subgroups congr...

Chapter VI of my old Springer Lecture Notes in Mathematics 789 Arithmetic Groups (1980) is in English and gives a version of H. Matsumoto's and C. Moore's arguments for the subgroups of $\operatorname …
Jim Humphreys's user avatar
3 votes

Computing Deligne-Lusztig Characters in General

I'm not quite sure what you are looking for, but Green's work (though combinatorial and influential) was only one of the inputs for the Deligne-Lusztig paper of 1976. It might help for example to …
Jim Humphreys's user avatar
5 votes

Existence of a weight of a representation in the fundamental Weyl chamber

The problem with your highlighted formulation is that it's wrong as stated, unless for example you require that an "irreducible" representation be finite dimensional or have an integral highest weight …
Jim Humphreys's user avatar
5 votes

Reference Request: Structure constants for G2

Probably the earliest reference is the 1956-58 Chevalley seminar, available online in typed format, which has been republished in 2005 as a typeset book edited by P. Cartier: see Chapter 21. (No speci …
Jim Humphreys's user avatar
2 votes
Accepted

cohomology of finite groups of lie type with coefficients in the adjoint module

This area of the subject is somewhat frustrating, since there is a lot of literature but not many satisfactory results involving the entire cohomology ring. For what it's worth, I'll point you to a …
5 votes
2 answers
435 views

Difference of adjacent dominant weights is a root?

The basic set-up here makes sense in the theory of abstract root systems if one brings (integral) weights into the picture, but it may be more natural to think about the classical characteristic 0 the …
Jim Humphreys's user avatar
8 votes
Accepted

Decomposition into Weyl modules

Your conclusion about direct sums is false. It's helpful here to have some examples in mind, such as a typical projective/injective module for the Lie algebra of $G:=\mathrm{SL}_2$, lifted to $G$. Th …
Jim Humphreys's user avatar
5 votes
Accepted

Recursive formula for inverse Kazhdan-Lusztig polynomials

The case of an affine Weyl group is apparently the only one which has been looked at closely. But it may be hard to answer your specific question. As far as I know, there are two relevant papers, …
Jim Humphreys's user avatar
2 votes

Computing the inner automorphism group of a finite Lie algebra

The main problem I see with this line of questioning is the lack of a clear definition of "inner automorphism group of a finite Lie algebra". Many Lie algebras don't occur as Lie algebras of linear …
Jim Humphreys's user avatar
3 votes
Accepted

Reduced decomposition for Weyl group elements which support a Bessel function

I'd be extremely surprised if such tables or database existed, mainly because the number of possible reduced decompositions for a Weyl group element tenda to grow very large as the rank increases. …
Jim Humphreys's user avatar
7 votes
Accepted

Reference request: Models of cuspidal representations of GL(n,k) where k is a finite field

For the finite groups GL$_n(\mathbb{F}_q)$ there is an early paper by Lusztig well worth checking out here. This predates his broader work on finite groups of Lie type with Deligne (1976), where they …
Jim Humphreys's user avatar
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 …
Jim Humphreys's user avatar
3 votes

Reference Request: Derived group of $\mathscr R_u(B)$

Let me add a few comments in community-wiki format. There doesn't seem to be a convenient reference, apart from the one in Digne-Michel which Jay Taylor cites. But even here, the authors don't give …

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