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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 …
David Hill's user avatar
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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 …
David Hill's user avatar
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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 …
David Hill's user avatar
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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 …
David Hill's user avatar
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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 …
David Hill's user avatar
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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 …
David Hill's user avatar
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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).
David Hill's user avatar
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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 …
David Hill's user avatar
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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 …
David Hill's user avatar
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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 …
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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 …
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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 $M$ …
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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 …
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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 …
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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 …
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