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Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.
12
votes
Can one easily pick out a basis of a simple Lie algebra after picking a convex order?
What you are trying to do is done in complete detail in Leclerc's paper "Dual canonical bases, quantum shuffles and q-characters" (MR) based on the paper "Standard Lyndon bases of Lie algebras and en …
7
votes
Accepted
Degenerate affine Hecke Algebra
The degenerate affine Hecke algebra $H(k)$ over a field $F$ is isomorphic (as a vector space) to the tensor product
$$
H(k)=^{\mathrm{v.s.}} FS_k \otimes F[x_1,\ldots,x_k]
$$
where $FS_k$ is the group …
6
votes
3
answers
1k
views
An application of Maschke's theorem
I've been teaching some elementary representation theory to undergraduates, and want to provide applications of Maschke's theorem to complex group algebras to present in class. In particular, I'd like …
5
votes
1
answer
683
views
Convex PBW bases
Given a reduced expression for the longest word $w_0$ in the Weyl group of $\mathfrak{g}=\mathfrak{n}^+\oplus\mathfrak{h}\oplus{n}^-$, one obtains a convex ordering on the set of positive roots, $\be …
4
votes
Accepted
Does Schur's Lemma hold in this case? Regular representations of $S_n$ over $\mathbb R$
Irreducible representations of $S_n$ are absolutely irreducible, meaning that they remain irreducible after extension of scalars. Therefore, if $V$ is irreducible as an $\mathbb{R} S_n$-module and $\p …
4
votes
Schur-Weyl duality
Let $V$ be the vector representation of $GL_n(\mathbb{C})$, and let $d\leq n$.
You want to see the multiplicities of a given irreducible $S_d$ module in $V^{\otimes d}$ in terms of the dimension of …
4
votes
Simple modules for $U_q(\mathfrak{sl}_n)$ at roots of unity
Look at the paper Quantum Affine Algebras at Roots of Unity of Chari and Pressley (published as https://doi.org/10.1090/S1088-4165-97-00030-7).
4
votes
Practical Ways to get Skew-Schur Functions
As this is a representation theory question, the connection to affine Hecke algebras deserves a few more words. The (degenerate) affine Hecke algebra, $H_d$ is isomorphic as a vector space to $\mathbb …
3
votes
Are there positive formulae for the inner product between elements of a Lie algebra represen...
Ben, my paper on the Shapovalov form does give a generating series for the entries of a Gram matrix in Corollary 3.4, and those entries are evidently positive. It is not very hard to deduce a q-versi …
3
votes
3
answers
244
views
When are PIMS and Irreducibles not in correspondence?
Let $A$ be an algebra over some field $k$. Let $K_P(A)$ be the Grothendieck group of the category of projective $A$-modules and $K_F(A)$ the category of finite dimensional $A$-modules. I've been told …
3
votes
What is known about the centraliser of the Hecke algebra in the affine Hecke algebra?
This is not a complete answer, but does give some information.
In addition to having an embedding of the Iwahori-Hecke algebra into the affine Hecke algebra, $\iota:H_n^{\mathrm{fin}}\hookrightarrow …
3
votes
semisimplicity of braid reps?
A complete analysis of this is given in the paper by Orellana-Ram. Actually, they consider the action of the affine braid group on $M\otimes V^{\otimes n}$, but you can recover your case by taking $M$ …
3
votes
Young's lattice and the Weyl algebra
Sasha Kleshchev's book "Linear and Projective Representations of Symmetric Groups" is the reference I'd suggest. Chapter 1 contains the connection with Young's lattice, and the subsequent chapters dev …
3
votes
When does Lusztig's canonical basis have non-positive structure coefficients?
Ben,
I have heard the same thing, but I have never seen an example. After thinking about it a bit, I came up with the following 'heuristic' reason why the structure constants should be positive for ha …
2
votes
Constructing a simple $A$-module
The representation theory of the Clifford algebra you are asking about can be understood using the theory of associative superalgebras. In this context, the irreducible $\mathbb{Z}_2$-graded represent …