All Questions
Tagged with reductive-groups spherical-varieties
10 questions
11
votes
1
answer
398
views
Finiteness of $H_1 \backslash G / H_2$ and the geometry of the orbits
Let $G$ be a connected reductive group over an algebraically closed field $k$. By the Bruhat decomposition, $P \backslash G/P \cong W_P \backslash W / W_P$ is a finite set for any parabolic subgroup $...
- 6,622
10
votes
1
answer
860
views
Bialynicki-Birula decompositions and fixed points
I was reading Luna's paper Toute variété magnifique est sphérique and stumbled on a few facts about Bialynicki-Birula decompositions and fixed points that I don't understand.
Here is the setup. Let $...
8
votes
2
answers
459
views
Spherical roots, restricted roots, and the dual group of a symmetric variety
Let $k$ be an algebraically closed field of characteristic $0$ and $G$ a semisimple simply-connected group over $k$. Consider a symmetric variety of the form $X=G/H$, for $H=G^\theta$ the fixed point ...
- 553
7
votes
1
answer
396
views
Is there a Chevalley map for spherical varieties?
If $G$ is a reductive group, $T$ a maximal torus and $W$ its Weyl group the Chevalley restriction theorem (in its "multiplicative" version) gives an isomorphism between the GIT quotient of $...
- 553
7
votes
1
answer
371
views
Gelfand pair, weakly symmetric pair, and spherical pair
I am a bit confused with the relations among Gelfand pairs, weakly symmetric pairs, and spherical pairs defined in the book "Harmonic analysis on commutative spaces" written by professor ...
- 951
5
votes
1
answer
138
views
Representations with finitely many nilpotent orbits
Let $G$ be a reductive group over $\mathbb{C}$ and let $V$ be a finite dimensional representation of $G$. We can define the ``nilpotent cone'' of $V$ as
$$\mathcal{N}(V):=\{ v\in V\;: \; 0\in\overline{...
- 2,516
5
votes
1
answer
138
views
Element of Weyl chamber contracting $\mathbb{A}^n_k$ to a point
Let $G$ be a connected reductive group over an algebraically closed field $k$ of characteristic 0. Fix a Borel subgroup $B$ and a maximal torus $T \subset B$. Let $P \subset G$ be a parabolic subgroup ...
4
votes
0
answers
118
views
Reference Request: Classification of spherical varieties by "Weyl group invariant fans"
Apologies in advance for the vague question.
Let $X$ be a spherical variety with the action of some reductive group $G$. I have been told in conversation several times that such spherical varieties ...
- 63
3
votes
1
answer
134
views
Connected components of a spherical subgroup from spherical data?
This question is in a similar spirit to this one by Mikhail Borovoi.
Let $G$ be a reductive group over $\mathbb{C}$ and let $X=G/H$ be a homogeneous spherical variety.
Losev proved that the spherical $...
- 2,516
3
votes
0
answers
135
views
Localizations of smooth spherical varieties at simple roots
Setup
Let $G$ be a (connected) reductive group over an algebraically closed field $k$, and fix a Borel subgroup
$B \subset G$ and a maximal torus $T \subset B$. Let $\lambda: \mathbb{G}_m \to T$ be a ...