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

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
17 votes
4 answers
1k views

Reference request: Grassmannian and Plucker coordinates in type B, C, D

Grassmannian $Gr(k,n)$ is the set of $k$-dimensional subspace of an $n$-dimensional vector space. What are the Grassmannian in types B, C, D? What are the analog of Plucker coordinates and Plucker rel …
Jianrong Li's user avatar
  • 6,201
16 votes
4 answers
2k views

Decompose tensor product of type $G_2$ Lie algebras.

Let $G$ be a semisimple Lie algebra over $\mathbb{C}$. Let $V(\lambda)$ be the irreducible highest weight module for $G$ with highest weight $\lambda$. If $G$ is of type A, we can decompose $V(\lambda …
Jianrong Li's user avatar
  • 6,201
14 votes
1 answer
560 views

Is there some relation between cluster algebras and crystal graphs?

Cluster algebras are closely related to totally positivity in algebraic groups and canonical bases in quantum groups. Is there some relation between cluster algebras and crystal graphs? Can the cryst …
Jianrong Li's user avatar
  • 6,201
10 votes
2 answers
1k views

Relations between affine Grassmannian and Grassmannian

Let $\mathcal K = k((t))$ be the field of formal Laurent series over $k$, and by $\mathcal O = k[[t]]$ the ring of formal power series over $k$. Let $G$ be an algebraic group over $k$. The affine Gr …
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
8 votes
1 answer
418 views

Compatibility conditions for Yetter-Drinfeld modules

In the paper, page 28, Definition 4.2.1, the compatibility condition for a Yetter-Drinfeld module over $H$ is $$ h_{(1)} v_{(-1)} \otimes h_{(2)}.v_{(0)} = (h_{(1)}.v)_{(-1)}h_{(2)} \otimes (h_{(1)}. …
Jianrong Li's user avatar
  • 6,201
7 votes
1 answer
181 views

How to translate multi-segments to Drinfeld polynomials?

Let $\hat{H}_m=\hat{H}_m(q)$ be the Iwahori-Hecke algebra of $GL_m$, see for example, Section 2. The simple $\hat{H}_m$-modules are parametrized by Zelevinsky's multi-segments, See Section 2.2 of the …
Jianrong Li's user avatar
  • 6,201
6 votes
3 answers
1k views

Reference request: representation of type G2 Lie algebras.

Let $\mathfrak{g}$ be an Lie algebra of type G2. Are there some combinatorial ways to describe a basis of a $\mathfrak{g}$-module? For classical types, there is a method used tableaux. Thank you very …
Jianrong Li's user avatar
  • 6,201
6 votes
1 answer
255 views

Questions about the $\mathbf{i}$-trails of Berenstein and Zelevinsky

The $\mathbf{i}$-trails of Berenstein and Zelevinsky was introduced on page 5 (Definition 2.1) in this paper. It is defined as follows. Let $\gamma, \delta \in \mathfrak{h}^*$. Let ${\bf i}=(i_1, \ldo …
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
6 votes
1 answer
297 views

What is the status of a problem about cluster categories?

Let $H$ be a hereditary algebra of Dynkin type. There is a cluster category $\mathcal{C}_H$ defined by Aslak Bakke Buan, Robert Marsh, Markus Reineke, Idun Reiten, and Gordana Todorov in Tilting theor …
Jianrong Li's user avatar
  • 6,201
5 votes
1 answer
423 views

Crystal basis for quantum groups and Lie algebras

Lie $g$ be a finite dimensional complex simple Lie algebra and $U_q(g)$ the corresponding quantum group, where $q$ is not a root of unity. Every simple finite dimensional $g$-module is of the form $V( …
Jianrong Li's user avatar
  • 6,201
5 votes
1 answer
297 views

Center of quantum affine algebras

Are there some references about the center of quantum affine algebras? I searched on google and only find the paper. In particular, what is the center of $U_q(\widehat{\mathfrak{sl}_2})$. Thank you ve …
Jianrong Li's user avatar
  • 6,201

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