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

3 votes
Accepted

Nicest coset representatives of the symplectic group in the general linear group

I suppose that "nice" is very much application-dependent, but let me give it a try. The first thing to notice is that, of course, you will not be able to find a global coset representative, since the …
José Figueroa-O'Farrill's user avatar
6 votes

The Category of Representations of a Group

In what sense is $SU(n)$ a finite group? Perhaps your question is about compact (including finite) groups? In that case, the representation theory is very well understood. For compact groups, my fa …
José Figueroa-O'Farrill's user avatar
5 votes

highest weight representation and electromagnetic fields

The 6-dimensional representation corresponding to the electromagnetic field is the realification of the symmetric square of the defining representation of $\mathrm{SL}(2,\mathbb{C})$, whose Lie algebr …
José Figueroa-O'Farrill's user avatar
3 votes
Accepted

Integrals of representations over geodesics

I had made a silly error in the first version of this answer. To try to answer your first question, notice that the image of $\gamma$ is a circle subgroup $T$, say, of $G$ and that the integral $I(\r …
José Figueroa-O'Farrill's user avatar
5 votes

References for traceless and/or imaginary Octonionic matrices?

You can put octonions inside a matrix, but this might not be a particularly fruitful thing to do since the octonion algebra is not associative. (So in particular you don't get octonionic Lie algebras …
José Figueroa-O'Farrill's user avatar
6 votes

What are the motivations for studying Cherednik (symplectic reflection, graded Hecke) algebras?

Although Vladimir already pointed a couple of relevant papers, there is also a more recent survey article by my colleague Iain Gordon on the arXiv: Symplectic reflection algebras, which you might find …
José Figueroa-O'Farrill's user avatar
1 vote

The meaning of an intertwiner?

By definition, an intertwiner between a representation $V$ to a representation $W$ of a group $G$, say, is a $G$-equivariant linear map from $V$ to $W$. In your example, assuming that $j_3 \in \lbrac …
José Figueroa-O'Farrill's user avatar
5 votes

Is there a definition of analogue Weyl group for Lie super algebra?

The answer to the question in the title is affirmative. In the Dictionary of Lie superalgebras, there is an entry on the Weyl group of a classical Lie superalgebra. It is generated by reflections as …
José Figueroa-O'Farrill's user avatar
2 votes

Radical of projection equals projection of radical?

I am not sure about infinite dimensions and/or positive characteristic, but the answer is Yes in the finite-dimensional, zero characteristic case. In your situation we have an exact sequence of Lie a …
José Figueroa-O'Farrill's user avatar
3 votes

On the full reducibility of representations of reductive Lie algebras

In many applications, a (real) reductive Lie algebra arises as the Lie algebra of a compact Lie group. In this case, and if the representation integrates to one of the group, then it is fully reducib …
José Figueroa-O'Farrill's user avatar
10 votes
2 answers
786 views

Is the category of representations of a finite W-algebra monoidal?

My question is prompted by Ben Webster's answer to this question. Is there a notion of tensor product for representations of a finite W-algebra? I thought about this question years ago in the contex …
José Figueroa-O'Farrill's user avatar
6 votes

ADE type Dynkin diagrams

They classify certain types of rational conformal field theories, as in this recent review paper.
José Figueroa-O'Farrill's user avatar
12 votes

Why would one expect a derived equivalence of categories to hold?

Disclaimer: I am not an expert. Curiously I just returned from a wonderful geometry seminar by Richard Thomas, who gave precisely a heuristic which addresses, perhaps if not your exact question, why …
3 votes

Symmetric matrices as a module over the skewsymmetric ones

I'm still not totally sure that this question is appropriate to the site, but since it seems to have generated some activity, perhaps I should expand on my cryptic comment concerning the irreducibilit …
José Figueroa-O'Farrill's user avatar
7 votes

Octonionic Unitary Group?

As others have pointed out, the nonassociativity of the octonions prevents one from constructing a group. For example, any subgroup of the octonions lives inside of a quaternion subalgebra. Having s …
José Figueroa-O'Farrill's user avatar

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