Skip to main content
Search type Search syntax
Tags [tag]
Exact "words here"
Author user:1234
user:me (yours)
Score score:3 (3+)
score:0 (none)
Answers answers:3 (3+)
answers:0 (none)
isaccepted:yes
hasaccepted:no
inquestion:1234
Views views:250
Code code:"if (foo != bar)"
Sections title:apples
body:"apples oranges"
URL url:"*.example.com"
Saves in:saves
Status closed:yes
duplicate:no
migrated:no
wiki:no
Types is:question
is:answer
Exclude -[tag]
-apples
For more details on advanced search visit our help page
Results tagged with
Search options not deleted user 391

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 …
Allen Knutson's user avatar
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 $(a_1,\ldots,a_{n-1})$ …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 $N$ …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar
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 …
Allen Knutson's user avatar

15 30 50 per page