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Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

2 votes

How do I stop worrying about root systems and decomposition theorems (for reductive groups)?

I don't really understand what you are asking for. Root systems are geometric objects associated to finite reflection groups. Try reading Jim Humphrey's "Reflection Groups and Coxeter Groups" for a ve …
The Amplitwist's user avatar
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 $M$ …
Glorfindel's user avatar
  • 2,821
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 Roberts's user avatar
  • 35.5k
1 vote

Noether's bound for anticommutative invariant theory (diff. forms instead of polynomials)?

There is a recent work of Weiqiang Wang and his student Jinkui Wan on spin-invariant theory. It appears to be the first of its kind.
darij grinberg's user avatar
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 …
LSpice's user avatar
  • 12.9k
2 votes

Request for classical articles in representation theory

Bernšteĭn, I. N.; Gelʹfand, I. M.; Gelʹfand, S. I. Differential operators on the base affine space and a study of $\mathfrak{g}$-modules. Lie groups and their representations (Proc. Summer School, Bol …
David Hill's user avatar
  • 1,472
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 …
David Hill's user avatar
  • 1,472
0 votes
Accepted

Decomposition of quadratic polynomials inti irreducible representations of affine group over...

I assume you mean to decompose $V$ into orbits since $V$ is only a $G$-set. I'm also going to guess that the action of $\alpha\in G=\mathbb{F}_p$ on $V$ is $\alpha.f(x)=f(x+\alpha)$. In this case, eve …
David Hill's user avatar
  • 1,472
0 votes
Accepted

Irreducible unitary representations of semidirect groups of a discrete abelian group by a di...

I would think that this result would go all the way back to Frobenius. Anyway, the proof seems easy enough: Let $V$ be the trivial $\Gamma$-module. We want to show that $\dim H_\Gamma=\dim\mathrm{Hom …
David Hill's user avatar
  • 1,472
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 …
2 votes

Given a locally nilpotent derivation over a field of characteristic 0 and a local slice, how...

Let $m$ be maximal such that $D^ma\neq 0$. Then, $$\Phi(a)=\frac{b}{(D\epsilon)^m}$$ where $$ b=\sum_{k=0}^m\frac{(-1)^k}{k!}(D^ka)(\epsilon)^k(D\epsilon)^{m-k}. $$ Now you need to show that $D(b)=0$. …
David Hill's user avatar
  • 1,472
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
  • 1,472
1 vote
Accepted

Homomorphisms from irreducible spaces to reducible spaces

I assume you are talking about representations of $S_n$ over $\mathbb{C}$. In this case, $\mathbb{C}S_n$ is left semi-simple by Maschke's Theorem, so every representation of $S_n$ is a direct sum of i …
David Hill's user avatar
  • 1,472
2 votes

A class of matrix determinants between Wronskians and Vandermondes

Couple of quick observations for $\alpha_i(x)=x^{(d_i)}$ ($x^{(d)}=x^d/d!$ as usual). Note that if $d_i>d_{i+1}$, for all $i$, then $G(x_1,\ldots,x_n)=0$ unless $d_i-d_{i+1}=1$. In particular, if th …
David Hill's user avatar
  • 1,472
1 vote
Accepted

classification of irreducible finite dimensional representation of affine hecke algebra of t...

This is done in Orellana-Ram, `Affine braids, Markov Traces and the category O'. The answer is essentially the same as for the degenerate affine Hecke algebra.
David Hill's user avatar
  • 1,472

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