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

1 vote

On a technical fact used in the proof of density of smooth vectors in a representation

Let me try to answer your question. Our problem is to determine what is the vector $\frac{d}{dt}|_{t=0}\exp(Y+tX)$. Let $L_{\exp Y}$ be the left translation by $\exp Y$. As you mentioned before, our …
Zhaoting Wei's user avatar
  • 9,019
1 vote
Accepted

Relationship between Verma modules and delta functions

In general cases Verma modules are corresponding to D-modules on flag variety and then via Riemann-Hilbert correspondence to constructible sheaves on flag variety. Hence the suitable generalization of …
Zhaoting Wei's user avatar
  • 9,019
5 votes
2 answers
915 views

Could we define the semi-direct product of two universal enveloping algebras?

If we have two Lie algebras $\mathfrak{g}$ and $\mathfrak{h}$ over a field $k$, and if we have a Lie algebra homomorphism $\mathfrak{g}\rightarrow \text{Der}_k(\mathfrak{h})$, then we can define the s …
Zhaoting Wei's user avatar
  • 9,019
10 votes
3 answers
632 views

Is the tensor product of two infinite dimensional objects in the BGG category $\mathcal{O}$ ...

Let $\mathfrak{g}$ be a finite dimensional complex semisimple Lie algebra (according to a comment of Victor Ostrik, we need to further require that $\mathfrak{g}$ is simple) and we can consider its BG …
Zhaoting Wei's user avatar
  • 9,019
4 votes
2 answers
787 views

What are the "tensor-closed" object of the BGG category $\mathcal{O}$ of a semisimple Lie al...

Let $\mathfrak{g}$ be a finite dimensional complex semisimple Lie algebra and we can consider its BGG category $\mathcal{O}$. It is well-known that $\mathcal{O}$ is not closed under tensor product, i. …
Zhaoting Wei's user avatar
  • 9,019
4 votes
0 answers
154 views

Is one of the hyperplane partitions of a irreducible root system always generate the whole W...

Let $\Delta$ be a irreducible root system and $\Delta^+$ be its positive roots. We say a subset $\Delta^{\prime}\subset \Delta^+$ can generate the Weyl group if reflections of roots in $\Delta^{\prim …
Zhaoting Wei's user avatar
  • 9,019
0 votes

Topological properties of $K$ orbits in $G/B$

For your question 2, the reason is in fact we can prove $$ K\times \mathfrak{p}\xrightarrow{\sim} G\\ (k,p)\mapsto k\exp(p) $$ is an diffeomorphism. Here $\mathfrak{p}$ is the $-1$ eigen space of the …
Zhaoting Wei's user avatar
  • 9,019
1 vote
1 answer
238 views

Can we have a nontrivial division of a irreducible root system as $\Phi=\Phi_{[\lambda]}\cup...

Let $(\mathfrak{g},\mathfrak{h},\Phi)$ be a root system of a complex simple Lie algebra, where $\Phi$ is the set of all roots. For each $\alpha\in \Phi$, let $\alpha^{\vee}=2\alpha/(\alpha,\alpha)$ be …
Zhaoting Wei's user avatar
  • 9,019
1 vote

Can we have a nontrivial division of a irreducible root system as $\Phi=\Phi_{[\lambda]}\cup...

I think the answer is yes because $(\Phi_{[\lambda]})^{\vee}$ and $(\Phi_{[\mu]})^{\vee}$ are closed sub-root systems of the dual root system $\Phi^{\vee}$. Closed means if $\alpha$ and $\beta$ are ro …
Zhaoting Wei's user avatar
  • 9,019
0 votes
1 answer
209 views

When does the Kazhdan-Lusztig polynomial $P_{x,w}(q)$ not vanish at $q=1$?

Let $\mathfrak{g}$ be a semisimple Lie algebra and $\mathfrak{h}$ be a Cartan subalgebra. For any $\lambda\in \mathfrak{h}^{*}$ let $M(\lambda)$ and $L(\lambda)$ be the Verma module and the simple mo …
Zhaoting Wei's user avatar
  • 9,019
7 votes
2 answers
417 views

About the map $S(\mathfrak{g}^ * )^G\rightarrow S(\mathfrak{h}^ * )^H$ for $H < G$

Let $G$ be a compact connected semisimple Lie group, $\mathfrak{g}$ be its complexified Lie algebra and $\mathfrak{g}^*$ its complex dual space. We can form the symmetric algebra $S(\mathfrak{g}^ * ) …
Zhaoting Wei's user avatar
  • 9,019
2 votes
1 answer
526 views

Kasparov's Dirac element and the index map

In Kasparov's 1988 paper Equivariant KK-theory and the Novikov conjecture section 4 he defined the Dirac element for a (non-spin) $G$- Riemanian manifold $X$ as an element in the $K$-homology $K^0_G(C …
Zhaoting Wei's user avatar
  • 9,019
8 votes
3 answers
694 views

What is the categorical significance of the trivial $\mathfrak{g}$-module in the category of...

This question may be trivial for experts. Let $\mathfrak{g}$ be a Lie algebra over a field $k$ and consider the category $\mathfrak{g}$-mod of $\mathfrak{g}$ modules. We can add suitable conditions, …
Zhaoting Wei's user avatar
  • 9,019
3 votes
0 answers
264 views

What's the relation of the Hecke algebra of a pair and the flag variety?

Let $G$ be a real semisimple Lie group and $K$ a maximal compact subgroup. Let $\mathfrak{g}$ and $\mathfrak{k}$ be the complexified Lie algebra of $G$ and $K$, respectively. Then the Hecke algebra …
Zhaoting Wei's user avatar
  • 9,019
4 votes
1 answer
197 views

Can we have a nontrivial division of a irreducible root system as the union of two closed su...

The question is related to this MO question. Let $(\Phi, E)$ be a irreducible crystallographic root system where $\Phi$ is the set of all roots and $E$ is the $\mathbb{R}$-span of $\Phi$. As in the st …
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  • 9,019

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