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Algebraic varieties with group operations given by morphisms, or group objects in the category of algebraic varieties, the category of algebraic schemes, or closely related categories.

42 votes
6 answers
7k views

Why we need to study representations of matrix groups?

Why we need to study representations of matrix groups? For example, the group $\operatorname{SL}_2(\mathbb F_q)$, where $\mathbb F_q$ is the field with $q$ elements, is studied by Drinfeld. I think th …
Jianrong Li's user avatar
  • 6,201
8 votes
1 answer
612 views

Bernstein–Zelevinsky classification for classical groups

Bernstein and Zelevinsky classifies the irreducible complex smooth representations of a general linear group over a local field in terms of cuspidal representations. The irreducible modules are parame …
Jianrong Li's user avatar
  • 6,201
8 votes
2 answers
954 views

Relation between representations of p-adic groups and affine Hecke algebras

Let $R_n$ be the category of complex-valued smooth finite-length representations of the group $GL_n(F)$, where $F$ is a local field. By the result of Borel, the subcategory of $R_n$ consisting of repr …
Jianrong Li's user avatar
  • 6,201
6 votes
2 answers
359 views

Questions about $\mathbb{C}[G/U^-]$ and $\mathbb{C}[B]$

Let $G = GL_n$. By algebraic Peter-Weyl theorem, we have $$ \mathbb{C}[G] = \bigoplus_{\lambda} V_{\lambda} \otimes V_{\lambda}^*, $$ where $\lambda$'s are dominant weights. Let $U^-$ be the unipote …
Jianrong Li's user avatar
  • 6,201
5 votes
1 answer
156 views

How to write the map $ℂ[G/U]↪ℂ[B]$ explicitly?

Let $G$ be a reductive algebraic group and $B$ a Borel subgroup of $G$. Let $T$ be a maximal torus of $G$ contained in $B$. The $B=UT=TU$ for some unipotent subgroup $U$ of $G$. We have Bruhat decompo …
Jianrong Li's user avatar
  • 6,201
3 votes
1 answer
312 views

What is $\rho^{\vee}(-1)$?

I am trying to understand the notation $\rho^{\vee}(-1)$. Let $T$ be a maximal torus of a semi-simple algebraic group $G$ and $\mathbb{G}_m$ the multiplicative group. I think that $\rho^{\vee}$ is a m …
Jianrong Li's user avatar
  • 6,201
3 votes
4 answers
358 views

References request: representations of classical groups

Are there some good references about representations of classical groups? What are the fundamental representations of classical groups of type $B, D$? I would like to know explicit formulas of the a …
Jianrong Li's user avatar
  • 6,201
3 votes
1 answer
484 views

What is the current status of representations of $GL_n(F)$ (and other algebraic groups)?

What is the current status of representations of $GL_n(F)$ (and other algebraic groups)? When $F$ is a local field, the representations of $GL_n(F)$ are classified by Bernstein and Zelevinsky in ter …
Jianrong Li's user avatar
  • 6,201
3 votes
0 answers
59 views

Kernel of the map $\mathbb{C}[G]^U \to \mathbb{C}[U^+]$

$\DeclareMathOperator{\SL}{\operatorname{SL}}$Let $G=\SL_k$ be the special linear group, $U$ the unipotent subgroup consisting of all lower unipotent triangular matrices, $U^+$ the unipotent subgroup …
Jianrong Li's user avatar
  • 6,201
2 votes
0 answers
80 views

Reference request: additive basis of $\mathbb{C}[N]$

Let $N$ be the maximal unipotent subgroup of $SL_k$. I think that the following is an additive basis of $\mathbb{C}[N]$: $$\{ e_T: T \text{ is a semi-standard Young tableau with at most $k-1$ rows and …
Jianrong Li's user avatar
  • 6,201
2 votes
0 answers
245 views

Reference request: proofs of the theorems in the paper "On the representation of the group G...

In the paper On the representation of the group $GL(n, K)$ where $K$ is a local field by Gelfand and Kazhdan, it is said that the proofs of the theorems in the paper are published in some other papers …
Jianrong Li's user avatar
  • 6,201
2 votes
0 answers
97 views

Can we write an element in a super Grassmannian as a pair of matrices?

Super Grassmannians are introduced by Manin, see for example. Elements in a grassmannian can be written as matrices, see for example. Can we write an element in a super Grassmannian as a pair of ma …
Jianrong Li's user avatar
  • 6,201
1 vote
0 answers
349 views

Borel subgroup of $Sp(4,\mathbb{C})$

I am trying to understand Borel subgroups of $Sp(4,\mathbb{C})$. I think that the following is a Borel subgroup of $Sp(4, \mathbb{C})$: the subset of $Sp(4, \mathbb{C})$ of all lower triangular matric …
Jianrong Li's user avatar
  • 6,201
1 vote
2 answers
147 views

How to decompose an map $\phi: \mathbb{G}_m \to T$ as the product of a cocharacter $\phi'$ a...

Let $\mathbb{G}_m$ be the multiplicative group and $T$ a maximal torus of a semisimple group. Let $X^*(T)=\{ \phi: T \to \mathbb{G}_m \}$ be the set of characters and $X_*(T)=\{ \phi^{\vee}: \mathbb{G …
Jianrong Li's user avatar
  • 6,201
1 vote
0 answers
36 views

What are the corner minors in $Sp(4)$?

This question relates to the question and the question. Let $B^-$ be the Borel subgroup of $Sp(4)$ consisting of all lower triangular matrices. Let $X = \left(\begin{array}{cccc} x_{1,1} & 0 & 0 & 0\ …
Jianrong Li's user avatar
  • 6,201

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