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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 …
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 …
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 …
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 …
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. …
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 …
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 …
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 …
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 …
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 …
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}^ * ) …
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 …
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, …
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 …
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 …