Index and stable linear forms of Lie algebras

Some properties of index of Lie algebras

In this paper we prove several theorems about the behavior of index of Lie algebras derived from associative algebras under tensor products of underlying associative algebras.

幂零李代数的指数

The index of nilpotent Lie algebras

本文研究多类幂零李代数的指数，并针对自由幂零、图及丝状幂零李代数给出显式计算公式。

Index of Graded Filiform and Quasi Filiform Lie Algebras

The filiform and the quasi-filiform Lie algebras form a special class of nilpotent Lie algebras. The aim of this paper is to compute the index and provide regular vectors of this two class of nilpotent Lie algebras. we consider the graded filiform Lie algebras $L_{n}$, $Q_{n}$, the $n$-dimensional filiform Lie algebras for $n$ $<8$, also the graded quasi-filiform Lie algebras and finally Lie algebras whose nilradical is $Q_{2n}$.

Indice des sous-algèbres biparaboliques d'une algèbre de Lie simple classique

We generalize the results in [2] giving a reduction algorithm allowing to compute the index of seaweed subalgebras of classical simple Lie algebras. We thus are able to obtain the index of some interesting families of seaweed subalgebras and to give new examples of large classes of Frobenius Lie algebras among them.

Meander graphs and Frobenius Seaweed Lie algebras

The index of a seaweed Lie algebra can be computed from its associated meander graph. We examine this graph in several ways with a goal of determining families of Frobenius (index zero) seaweed algebras. Our analysis gives two new families of Frobenius seaweed algebras as well as elementary proofs of known families of such Lie algebras.

The centralisers of nilpotent elements in classical Lie algebras

The index of a finite-dimensional Lie algebra $g$ is the minimum of dimensions of stabilisers $g_α$ of elements $α\in g^*$. Let $g$ be a reductive Lie algebra and $z(x)$ a centraliser of a nilpotent element $x\in g$. Elashvili has conjectured that the index of the centraliser $z(x)$ equals the index of $g$, i.e., the rank of $g$. Here Elashvili's conjecture is proved for reductive Lie algebras of classical type. It is shown that in cases $g=gl_n$ and $g=sp_{2n}$ the coadjoint action of $z(x)$ has a generic stabiliser. Also, we give an example of a nilpotent element $x\in so_8$ such that the co…

经典李代数的 nilpotent 轨道在 negation 下的稳定性

Nilpotent orbits of classical Lie algebras stable under negation

本文研究经典李代数中 nilpotent 轨道在 negation 下的稳定性，证明在这些轨道上不存在 Gibbs 状态，并对所有经典李代数进行了分类。

Notes sur l'indice des algèbres de Lie (I)

This article contains: - Proofs of certain results recently obtained by D. Panyushev. - An addendum to the "inequality of Panyushev". - Calculations of indexes of certain contracted Lie algebras. - Examples of additivity of the index of Lie algebras. ----- On trouvera dans ce papier : - Des démonstrations de certains des résultats obtenus récemment par D. Panyushev. - Un complément portant sur "l'inégalité de Panyushev''. - Des calculs d'indices de certaines contractées d'algèbres de Lie. - Des exemples d'additivité de l'indice des algèbres de Lie.

The index of a Lie algebra, the centraliser of a nilpotent element, and the normaliser of the centraliser

In this paper, we study the index for several natural classes of non-reductive subalgebras of semisimple Lie algebras. Namely, we look at parabolic subalgebras, centralisers of nilpotent elements, and the normalisers of the centralisers. We discuss a conjecture of Elashvili to the effect that the index of any centraliser is equal to the rank of the semisimple algebra in question. It is shown that Elashvili's conjecture is true for `small' and `large' orbits. Some properties of the index for the normaliser of the centraliser are proved. In particular, we prove that, for a regular nilpotent elem…

On associative algebras with unity and Lie index 1

We present a new method of analysis of associative algebras. This method bears a certain resemblance to the famous analysis of commutative $C^*$-algebras in which an important role is played by multiplicative functionals over the algebra. These functionals can be considered as "rank 1" in the framework of our method. In our approach a special position is taken by generic (maximal rank) functionals, which reveal a wealth of information on the structure of non-commutative algebras. We apply this method to derive interesting properties of index of Lie algebras and to analyze finite-dimensional as…

The index complex of a maximal subalgebra of a Lie algebra

Let M be a maximal subalgebra of the Lie algebra L. A subalgebra C of L is said to be a completion for M if C is not contained in M but every proper subalgebra of C that is an ideal of L is contained in M. The set I(M) of all completions of M is called the index complex of M in L. We use this concept to investigate the influence of the maximal subalgebras on the structure of a Lie algebra, in particular finding new characterisations of solvable and supersolvable Lie algebras.

指数为$2n$的正规李子群的Fubini定理

The Fubini Theorem for Normal Lie Subgroups of Index $2n$

该研究先证明指数为2n的正规子群与对合元生成的群的半直积分解结构，再用该结论推导紧李群中指数为2n子群的Fubini定理，并给出其在不变量理论中的应用。

群代数中斜对称元的李幂零指数

Lie nilpotency index of skew symmetric elements in group algebras

针对换位子群阶为$p$的有限奇素数$p$-群$G$的群代数，证明其李幂零指数由斜对称元构成的李子代数决定，并描述了该子代数的下李中心序列结构。

Good index behaviour of $θ$-representations, I

Let $Q$ be an algebraic group with $q=\Lie Q$ and $V$ a $Q$-module. The index of $V$ is the minimal codimension of the $Q$-orbits in the dual space $V^*$. There is a general inequality, due to Vinberg, relating the index of $V$ and the index of a $Q_v$-module $V/q.v$ for $v\in V$. A pair $(Q,V)$ is said to have GIB if Vinberg's inequality turns into an equality for all $v\in V$. In this article, we are interested in the GIB property of $θ$-representations, where $θ$ is a finite order automorphism of a simple Lie algebra $g$. An automorphism of order $m$ defines a $Z/mZ$-grading $g=g_0+g_1+...+…

A Lie-algebraic approach to the local index theorem on compact homogeneous spaces

Using a K-theory point of view, Bott related the Atiyah-Singer index theorem for elliptic operators on compact homogeneous spaces to the Weyl character formula. This article explains how to prove the local index theorem for compact homogenous spaces using Lie algebra methods. The method follows in outline the proof of the local index theorem due to Berline and Vergne. But the use of Kostant's cubic Dirac operator in place of the Riemannian Dirac operator leads to substantial simplifications. An important role is also played by the quantum Weil algebra of Alekseev and Meinrenken.

Sur l'indice des sous-algèbres biparaboliques de $\mathfrak{gl}(n)$

We give some properties on the index of seaweed subalgebras of the complex Lie algebra $\mathfrak{gl}(n)$ which allow to obtain formulas for the index of some interesting classes of this family and to give new families of Frobenius Lie algebras.

On the sum of the index of a parabolic subalgebra and of its nilpotent radical

In this short note, we investigate the following question of Panyushev : ``Is the sum of the index of a parabolic subalgebra of a semisimple Lie algebra $\mathfrak{g}$ and the index of its nilpotent radical always greater than or equal to the rank of $\mathfrak{g}$?''. Using the formula for the index of parabolic subalgebras conjectured by Tauvel and the author, and proved by Millet-Fauquant and Joseph, we give a positive answer to this question. Moreover, we also obtain a necessary and sufficient condition for this sum to be equal to the rank of $\mathfrak{g}$. This provides new examples of d…

李超代数的Borel子代数的指标

On the Index of Borel Subalgebras of Lie Superalgebras

本文针对复数域上基础经典李超代数的Borel子代数，通过扩展强正交根与Kostant cascade理论到广义根系理论，给出其指标的上界并证明相关指标为0的结论。

Stability for biparabolic subalgebras of simple Lie algebras

Let K be an algebraically closed field of characteristic 0. It is well known that any quasi-reductive Lie algebra is stable. However, there are stable Lie algebras which are not quasi-reductive. This raises the question, if for some particular class of non-reductive Lie algebras, there is equivalence between stability and quasi-reductivity. In particular, it was conjectured by Panyushev that these two notions are equivalent for biparabolic subalgebras of a reductive Lie algebra. In this paper, we give a positive answer to this conjecture.

Indice et decomposition de Cartan d'une algebre de Lie semi-simple reelle

The Iwasawa decomposition $\mathfrak{g}=\mathfrak{k}_0 \oplus \hat{\mathfrak{a}}_0 \oplus \mathfrak{n}_0$ of the real semisimple Lie algebra $\mathfrak{g}_0$ comes from its Cartan decomposition $\mathfrak{g}_0=\mathfrak{k}_0 \oplus \mathfrak{p}_0$. Then we get $\mathfrak{g}_0=\mathfrak{k}_0 \oplus \mathfrak{b}_0$ where $\mathfrak{b}_0=\hat{\mathfrak{a}}_0 \oplus \mathfrak{n}_0$. The question of knowing if the index were additive in the decomposition $\mathfrak{g}_0=\mathfrak{k}_0 \oplus \mathfrak{b}_0$ goes back M. Raïs \cite{Rais}. In \cite{Moreau3}, I wrote that the index always is additive …

Indice du normalisateur du centralisateur d'un element nilpotent dans une algebre de Lie semi-simple

The index of a complex Lie algebra is the minimal codimension of its coadjoint orbits. Let us suppose $\g$ semisimple, then its index, ${\rm ind} \g$, is equal to its rank, ${\rm rk \g}$. The goal of this paper is to establish a simple general formula for the index of $\n(\g^ξ)$, for $ξ$ nilpotent, where $\n(\g^ξ)$ is the normaliser in $\g$ of the centraliser $\g^ξ$ of $ξ$. More precisely, we have to show the following result, conjectured by D. Panyushev \cite{Panyushev} : $${\rm ind} \n(\g^ξ) = {\rm rk \g}-\dim \z(\g^ξ),$$ where $\z(\g^ξ)$ is the center of $\g^ξ$. D. Panyushev obtained in \ci…

Lie nilpotency indices of modular group algebras

Let K be a field of positive characteristic p and KG the group algebra of a group G. It is known that if KG is Lie nilpotent then its upper (or lower) Lie nilpotency index is at most |G'|+1, where |G'| is the order of the commutator subgroup. The class of groups G for which these indices are maximal or almost maximal have already been determined. Here we determine G for which upper (or lower) Lie nilpotency index is the next highest possible.

分次李代数的特征层：稳定分次

Character Sheaves for Graded Lie Algebras: Stable Gradings

本研究针对稳定分次李代数，通过分析[GVX2]中邻近周期层的傅里叶变换，构造出推测为尖点特征层的满支撑特征层，涉及单位根处复反射群相关Hecke代数的不可约表示。

Stable invariance of the restricted Lie algebra structure of Hochschild cohomology

We show that the restricted Lie algebra structure on Hochschild cohomology is invariant under stable equivalences of Morita type between self-injective algebras. Thereby we obtain a number of positive characteristic stable invariants, such as the $p$-toral rank of $\mathrm{HH}^1(A,A)$. We also prove a more general result concerning Iwanaga-Gorenstein algebras, using a more general notion of stable equivalences of Morita type. Several applications are given to commutative algebra and modular representation theory. These results are proven by first establishing the stable invariance of the $B_\i…

Quantization of branching coefficients for classical Lie groups

We study natural quantizations of branching coefficients corresponding to the restrictions of the classical Lie groups to their Levi subgroups. We show that they admit a stable limit which can be regarded as a $q$-analogue of a tensor product multiplicity. According to a conjecture by Shimozono, the stable one-dimensional sum for nonexceptional affine crystals are expected to occur as special cases of these $q$-analogues.

Lie quasi-states

Lie quasi-states on a real Lie algebra are functionals which are linear on any abelian subalgebra. We show that on the symplectic Lie algebra of rank at least 3 there is only one continuous non-linear Lie quasi-state (up to a scalar factor, modulo linear functionals). It is related to the asymptotic Maslov index of paths of symplectic matrices.

Stable flatness of nonarchimedean hyperenveloping algebras

Let L be a p-adic local field and g a finite dimensional Lie algebra over L. We show that its hyperenveloping algebra F(g) is a stably flat completion of its universal enveloping algebra. As a consequence the relative cohomology for the locally convex algebra F(g) coincides with the underlying Lie algebra cohomology. Final version. Some minor items corrected. Appeared in Journal of Algebra (2010).

Metric Lie algebras with maximal isotropic centre

We investigate a certain class of solvable metric Lie algebras. For this purpose a theory of twofold extensions associated to an orthogonal representation of an abelian Lie algebra is developed. Among other things, we obtain a classification scheme for indecomposable metric Lie algebras with maximal isotropic centre and the classification of metric Lie algebras of index 2.

On the crystal graph description of the stable Weyl group multiple Dirichlet series

For a semisimple Lie algebra admitting a good enumeration, we prove a parametrization for the elements in its Weyl group. As an application, we give a coordinate-free comparison between the crystal graph description (when it is known) and the Lie-theoretic description of the Weyl group multiple Dirichlet series in the stable range.

求解（弯曲）Bernstein-Gelfand-Gelfand序列的指标问题

Solving the index problem for (curved) Bernstein-Gelfand-Gelfand sequences

本文研究抛物几何中弯曲 BGG 序列的指标问题，利用 Heisenberg 演算给出其嵌入 G-等变 K-同调的条件，并证明该方法对更高秩李群失效。

Euler characteristic of stable envelopes

In this paper we prove a formula relating the equivariant Euler characteristic of $K$-theoretic stable envelopes to an object known as the index vertex for the cotangent bundle of the full flag variety. Our formula demonstrates that the index vertex is the power series expansion of a rational function. This result is a consequence of the 3d mirror self-symmetry of the variety considered here. In general, one expects an analogous result to hold for any two varieties related by 3d mirror symmetry.