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Lie algebras are algebraic structures which were introduced to study the concept of infinitesimal transformations. The term "Lie algebra" (after Sophus Lie) was introduced by Hermann Weyl in the 1930s. In older texts, the name "infinitesimal group" is used. Related mathematical concepts include Lie groups and differentiable manifolds.

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
8 votes
1 answer
1k views

PBW basis and canonical basis

Consider the example of $\mathfrak{g} = sl_3$. Then $$ \mathfrak{g} = \mathfrak{n} \oplus \mathfrak{h} \oplus \mathfrak{n}^{-}, $$ where $\mathfrak{n}$ is generated by $E_{12}, E_{13}, E_{23}$, $\mat …
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 …
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  • 6,201
5 votes
0 answers
218 views

Reference about the root systems $E_{n}$, $n \ge 10$

I am trying to understand the root systems $E_{n}$, $n \ge 10$. In particular, I would like to find some references which describe the number of real roots and imaginary roots of a given degree. Cons …
Jianrong Li's user avatar
  • 6,201
5 votes
1 answer
194 views

Number of real roots in type $\tilde{E}_8$

Let $\Phi_+$ be the set of all positive roots for a Kac-Moody algebra. Denote by $\alpha_i$ the simple root associated with node $i$ by for $i \in \{1, \ldots, n-1\}$ and by $\beta$ the simple root as …
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  • 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
4 votes
2 answers
690 views

Compute formal character of semisimple Lie algebras.

Let $\mathfrak{g}$ be a semisimple Lie algebra and $V_{\lambda}$ be the irreducible $\mathfrak{g}$-module with highest weight $\lambda$. Are there some softwares which can compute the formal character …
Jianrong Li's user avatar
  • 6,201
4 votes
1 answer
428 views

Faithful linear representation of a nilpotent Lie algebra

Let \begin{align} \mathfrak{g} = Span_{\mathbb{C}}\{ e_1, e_2, e_3, e_4, e_5: \text{ non-zero brackets are } [e_1, e_i]=e_{i+1}, i=2,3,4, [e_2, e_3]=e_5 \} \end{align} be a $5$-dimensional Lie algebr …
Jianrong Li's user avatar
  • 6,201
4 votes
1 answer
865 views

How to show that the graded dual of the universal enveloping algebra of a free Lie algebra o...

In the article, the universal enveloping algebra of a free Lie algebra on a set X is defined to be the free associative algebra generated by X. It is said that the graded dual of the universal envel …
Jianrong Li's user avatar
  • 6,201
4 votes
0 answers
301 views

Does the tensor algebra $T(V)$ of $V$ isomorphic to the symmetric algebra of the free Lie al...

Let $V$ be a finite dimensional vector space. Let $T(V)$ be the tensor algebra over $V$. Do we have $T(V) \cong S(Lie(V))$ as a graded vector space? Here $S(Lie(V))$ is the symmetric algebra of the …
Jianrong Li's user avatar
  • 6,201
4 votes
2 answers
486 views

Classifications of Lie bialgebras

What is the current status of the classifications of Lie bialgebras? In particular, has the following problem been solved? Let $gl_n$ be the general linear Lie algebra. Classify all Lie cobrackets $\d …
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  • 6,201
3 votes
0 answers
134 views

How to understand extremal vector?

Extremal vectors are defined in Kashiwara's paper. The definition is as follows. Simple reflections in the Weyl group of $\mathfrak{g}$ acts on the crystal basis of integrable $U_q(\mathfrak{g})$-mo …
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  • 6,201
3 votes
1 answer
383 views

Modules which are direct sum of weight spaces.

For a semisimple Lie algebra $\mathfrak{g}$, a highest weight module $V(\lambda)$ with highest weight weight $\lambda$ has the property that every submodule $W$ of $V(\lambda)$ is a direct sum of the …
Jianrong Li's user avatar
  • 6,201
3 votes
1 answer
149 views

Are all the Lie bialgebra structure on $sl_n$ coboundary?

In the case of $sl_2$, there are three Lie bialgebra structures. We have three cobrackets $\delta: sl_2 \to \Lambda^2 sl_2$. Each $\delta$ can be written as $\delta=d r$ for some matrix $r$. Therefore …
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