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

18 votes
3 answers
2k views

Hopf dual of the Hopf dual

Given any Hopf algebra $A$ over a field $k$, one can also define the Hopf dual $A^*$ of as follows: Let $A^∗$ be the subspace of the full linear dual of $A$ consisting of elements that vanish on some …
Nadia SUSY's user avatar
6 votes
2 answers
1k views

Non-faithful irreducible representations of simple Lie groups

For a complex simple Lie algebra $\frak{g}$, which of its finite dimensional irreducible representations give non-faithful representations of the corresponding simply-connected compact Lie group. Mor …
Nadia SUSY's user avatar
18 votes
2 answers
4k views

What is a tensor category?

A monoidal category is a well-defined categorical object abstracting products to the categorical setting. The term tensor category is also used, and seems to mean a monoidal category with more structu …
Nadia SUSY's user avatar
6 votes
1 answer
319 views

Branching from $E(6)$ to $SO(10) \times U(1)$

In $E(6)$ inspired models of supersymmetry, the inclusion of Lie subgroups $$ SO(10) \times U(1) \hookrightarrow E_6 $$ is important object of interest. See here for my motivating example. In partic …
Nadia SUSY's user avatar
4 votes
2 answers
403 views

GAP versus SageMath for branching to Lie subgroups

Which computer package is better, GAP or SageMath, for decomposing an irreducible representation of a (simple) Lie group $G$ into representations of a Lie subgroup. I am most interested when branchi …
Nadia SUSY's user avatar
4 votes
1 answer
242 views

Decomposing tensor powers of the fundamental representation of exceptional Lie algebras

For the $A$-series, tensor powers of the fundamental representation of $\frak{sl}_n$ decompose into irreducibles according to a certain Young diagram/ partition formula. This inspires, for example, th …
Nadia SUSY's user avatar
9 votes
1 answer
438 views

Young tableaux for exceptional Lie algebras

Irreducible representations for the $A$-series Lie algebras are labelled Young diagrams, with a basis of each given by Young tableaux. Moreover, analogues exist for the $B,C$, and $D$ series. Does su …
Nadia SUSY's user avatar
4 votes
Accepted

Weyl's Branching Rule for $SU(N)$-Setting

The question is answered on page 385 of the classical Zhelobenko book Compact Lie groups and their representations for the more general case of $SU(n+m)/SU(n) \times SU(m)$.
Nadia SUSY's user avatar
4 votes
1 answer
202 views

Branching to Levi subgroups in SAGE and the circle action

In the SAGE computer package, there useful exist tools for branching representations of a simple Lie group to a Levi subgroup: http://doc.sagemath.org/html/en/reference/combinat/sage/combinat/root_sy …
Nadia SUSY's user avatar
5 votes
3 answers
836 views

Weyl's Branching Rule for $SU(N)$-Setting

On the Wikipedia page for restricted representations https://en.wikipedia.org/wiki/Restricted_representation there is presented a number of explicit "branching rules". In particular, there is the W …
Nadia SUSY's user avatar
11 votes
4 answers
2k views

The tensor product of two monoidal categories

Given two monoidal categories $\mathcal{M}$ and $\mathcal{N}$, can one form their tensor product in a canonical way? The motivation I am thinking of is two categories that are representation categor …
Nadia SUSY's user avatar