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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 …
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 $M$ …
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).
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.
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 …
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 …
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 …
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 …
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 …
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 $D(b)=0$. …
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 …
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 …
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 …
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.