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Lie Groups are Groups that are additionally smooth manifolds such that the multiplication and the inverse maps are smooth.
2
votes
Verma modules and Borel–Weil
I don't think the $\pm$ issue is too deep, and I'm punting on it in favor of answering the other question.
You can get a hold of dual Verma modules by considering distributions on $G/B$ supported on a …
4
votes
Weyl's Branching Rule for $SU(N)$-Setting
Every irrep of $SU(n)$ extends to irreps of $U(n)$, and conversely, the restriction of any irrep of $U(n)$ to $SU(n)$ remains irreducible. If your dominant weight of $SU(n)$ is $(a_1,\ldots,a_{n-1})$ …
17
votes
Reference request: Grassmannian and Plucker coordinates in type B, C, D
What these have in common is that they are of the form $G/P$ for $P$ a maximal parabolic. As such each has a minimal projective embedding of the form $G/P \hookrightarrow \mathbb P(V_\omega)$ where $V …
7
votes
0
answers
149
views
Eigenspaces and covering relations of twisted involutions
Let $\theta:G\to G$ be an involution of a complex connected reductive Lie group, preserving a maximal torus $T$ (which, for me, lies inside a $\theta$-invariant Borel $B$). Let $K = G^\theta$ be the f …
2
votes
Accepted
Is the action $T \times G \to G$ Poisson?
Ingredients:
The composite of Poisson maps is Poisson
The action map $G\times G\to G$ is Poisson
Your choice of $T,U$ should be Poisson submanifolds of $G$. You didn't say which Poisson structure yo …
1
vote
Question on irreducible representation of tensor products
Your question is about the vectors in $V_1\otimes V_2$ that provide $1$-dimensional $B_\Delta$-subrepresentations of weight $\mu$, where $B_\Delta$ is the diagonal in $B\times B \leq G\times G$. Let's …
4
votes
The Analog of Borel Subgroup in a Compact Real Form
It sounds like you want a datum to associate to a compact Lie group and chosen torus, that's functorially the same as a choice of Borel containing that torus if one were to complexify, without using t …
5
votes
Dimension of the zero weight space in $V_{2\rho}$
In general, $V_{k\rho} \cong \bigotimes\limits_{\beta\in \Delta_+} (\mathbb C_{k\beta/2} \oplus \mathbb C_{(k-2)\beta/2} \oplus \ldots \oplus \mathbb C_{-k\beta/2})$ as $T$-representations, provable v …
3
votes
How can one show $G/T$ is a coadjoint orbit for a compact Lie group $G$ and $T$ its maximal ...
Use the Haar measure on $G$ (compact!) to average a metric, obtaining a $G\times G$-invariant metric, and thus an identification $\mathfrak g \cong \mathfrak g^*$. Also, the geodesic spray $\mathfrak …
6
votes
Accepted
Motivating the existence of Canonical Bases for Representations
I don't really see how to get there from just compact groups, so in that sense this is not an answer. My take on the question is something like: how might one have guessed the existence of canonical b …
7
votes
How to write $\mathbb{C}[G/U_-]=\oplus_{\lambda} V_{\lambda}$ explicitly?
It's slightly nicer to look at $M_n // U_-$ instead of $GL(n) // U_-$, since then we're looking at a subring of invariants inside a polynomial ring. Namely,
the subring generated by all determinants t …
10
votes
Representation viewpoint on Chern–Weil (cohomology computations done with rep theory?)
The construction you describe appears in Tamvakis' The connection between representation theory and Schubert calculus (Enseign. Math. 50 (2004), 267-2860). Basically, instead of working with represent …
3
votes
Orientability of orbit type strata of Lie group actions
In your question, you may as well take $M=M_j=$ a ($G$-invariant) tubular neighborhood of a single orbit $G/S$. Near the point $S/S$, the space looks like $\mathfrak g/\mathfrak s \times N$, where $N$ …
2
votes
Is there a formula for the Frobenius-Schur indicator of a rep of a Lie group?
This is not a complete answer, but grew large for a comment.
Duality acts on the simple weights $\{\omega_i\}$, by $-w_0$ (where $w_0$ is the long element of the Weyl group), so we should really grou …
4
votes
Accepted
Canonical class of partial flag variety
If $G$ is simply connected (so, $SL_n$ in your less general question), then every line bundle $\mathcal L$ is uniquely of the form $G \times^B \mathbb C_\lambda$ where $\mathbb C_\lambda$ is the $T$-i …