Ivan Marin
For any $n \geq 3$ we obtain the decomposition in simple factors of the Lie subalgebra of the group algebra of the symmetric group on $n$ letters generated by the transpositions. This enables us to determine the algebraic hull of the braid group $\B_n$ and of several of its subgroups inside the representations of the Iwahori-Hecke algebra of type A.
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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.
This text is a continuation to "Notes sur l'indice des algèbres de Lie (I)", math.RT/0605499 ----- Ce texte est une suite à : "Notes sur l'indice des algèbres de Lie (I)".
Soit F un corps local non archimedien de caracteristique residuelle p. On designe par R un corps algebriquement clos de caracteristique p et par Q une cloture algebrique du corps des nombres p-adiques. On classifie les modules simples de dimension finie de la R-algebre de Hecke-Iwahori du groupe lineaire Gl_3(F). Ils sont obtenus par reduction modulo p des modules simples de la Q-algebre de Hecke-Iwahori qui possedent une structure entiere.
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.
Ce mémoire traite de la théorie des représentations d'une certaine classe d'algèbres de Lie de dimension infinie, les algèbres de courants tordues. L'objet du travail est d'obtenir une classification des blocs d'extensions d'une catégorie de modules de dimension finie pour une algèbre de courants tordue donnée. Les principales sources de cette étude sont les récentes classifications des modules simples de dimension finie pour ces algèbres et des blocs d'extensions pour les modules de dimension finie dans le cas des algèbres d'applications équivariantes. Ces algèbres de courants tordues compren…
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.
Formal actions of Lie algebras over vector spaces are introduced in a purely algebraic way, as a mimic of infinitesimal operations of Banach Lie algebras over Banach analytic manifolds. In analogy with the case of abstract groups, complete wreath products and triangular actions are then defined for Lie algebras acting "en cascade" over vector spaces. Finally, a Kaloujnine-Krasner type theorem for Lie algebra extensions is proved. ----- En mimant les lois d'opérations infinitésimales des algèbres de Lie sur les variété s analytiques banachiques, on introduit de manière purement algèbrique la no…
For a simply connected semisimple algebraic group over an algebraically closed field of positive characteristic we have already constructed a splitting of the Frobenius endomorphism on its algebra of distributions. We generalize the construction to the case of general reductive groups and derive the corresponding corollaries.
If V is a simple complex euclidean Jordan algebra and G the subgroup of GL(V) fixing the determinant of V, we give a unified description of the invariant algebras C[pV]^G, for p not greater than three.
Sergey Fomin and Andrei Zelevinsky have invented cluster algebras at the beginning of this decade with the aim of creating an algebraic framework for the study of canonical bases in quantum groups and total positivity in algebraic groups. It soon turned out that the combinatorics of cluster algebras also appear in many other subjects and notably in the representation theory of quivers and finite-dimensional algebras. In this talk, we give a concise introduction to cluster algebras and sketch two significant applications concerning the study of certain discrete dynamical systems and the constru…
This manuscript synthesizes almost fifteen years of research in algebraic combinatorics, in order to highlight, theme by theme, its perspectives. In part one, building on my thesis work, I use tools from commutative algebra, and in particular from invariant theory, to study isomorphism problems in combinatorics. I first consider algebras of graph invariants in relation with Ulam's reconstruction conjecture, and then, more generally, the age algebras of relational structures. This raises in return structural and algorithmic problems in the invariant theory of permutation groups. In part two, th…
We consider the space of tensor densities on the n-dimensional sphere with degree lambda (or, equivalently, of conformal densities with degree lambda). This space is a module over the group of diffeomorphisms, and consequently over the Lie algebra of vector fields, on the sphere, and we first prove that as a module over the conformal group, it is infinitesimally equivalent to an induced module from the principal series, precisely from the nonunitary spherical series on the space of smooth functions on the sphere. In function of lambda,(g,K)-simple and unitary submodules of the space of tensor …
Opérateurs d'entrelacement et algèbres de Hecke avec paramètres d'un groupe réductif $p$-adique - le cas des groupes classiques
本文研究了p-adic简约群的缠结算子与Hecke代数的参数化问题，通过计算诱导项目生成元的终等代数，证明其同构于Hecke代数与有限群代数的半直接积。
Let $\mathbb{K}$ be an algebraically closed field of characteristic 0. A finite dimensional Lie algebra $\mathfrak{g}$ over $\mathbb{K}$ is said to be stable if there exists a linear form $g\in\mathfrak{g}^{*}$ and a Zariski open subset in $\mathfrak{g}^{*}$ containing $g$ in which all elements have their stabilizers conjugated under the connected adjoint group. 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 equiv…
Full details are given for the definition and construction of the wreath product of two arbitrary Lie algebras, in the hope that it can lead to the definition of a suitable Lie group to be the wreath product of two given Lie groups. In the process, quite a few new notions are needed, and introduced. Such are, for example : Formal series with variables in a vector space and coefficients in some other vector space. Derivation of a formal series relative to another formal series. The Lie algebra of a vector space. Formal actions of Lie algebras over vector spaces. The basic formal action of a Lie…
The Lie superalgebra of transpositions
本文将对称群的群代数视为超代数，描述了由对换生成的李子超代数，并更正了第4.5至4.7节的部分论证，主要结果不受影响。
We consider a nonlinear representation of a Lie algebra which is regular on an abelian ideal, we define a normal form which generalizes that defined in [D. Arnal, M. Ben Ammar, M. Selmi, {\rm Normalisation d'une représentation non linéaire d'une algèbre de Lie}. {\it Annales de la Faculté des Sciences de Toulouse}, 5e série, tome 9, No 3, 1988, p 355--379.]
On homomorphisms between Weyl modules: The case of a column transposition
本文分类了线性群在列对换划分下 Weyl 模间的同态，证明其非零当且仅当 $p=2$ 且 $a$ 为偶数，给出了维数为 1 的显式生成元，并指出其一般非 Carter-Payne 同态的复合。
Let k be an algebraically closed field of characteristic 0. We conclude the classification of finite dimensional pointed Hopf algebras whose group of group-likes is S_4. We also describe all pointed Hopf algebras over S_5 whose infinitesimal braiding is associated to the rack of transpositions.
Let G be a split simple group of type G_2 over a field k, and let g be its Lie algebra. Answering a question of Colliot-Thélène, Kunyavskiĭ, Popov, and Reichstein, we show that the function field k(g) is generated by algebraically independent elements over the field of adjoint invariants k(g)^G. Soit G un groupe algébrique simple et déployé de type G_2 sur un corps k. Soit g son algèbre de Lie. On démontre que le corps des fonctions k(g) est transcendant pur sur le corps k(g)^G des invariants adjoints. Ceci répond par l'affirmative à une question posée par Colliot-Thélène, Kunyavskiĭ, Popov et…
To a spetsial complex reflection group, equipped with a root lattice in the sense of Nebe, we attach a certain finite set playing a role which is analogous to the role of the set of unipotent classes of an algebraic group. In the case of imprimitive groups, we give a combinatoric parametrization of it in terms of Malle-Shoji generalized symbols. This result provides a link between the works of Shoji on Green functions for complex reflection groups and of Broue, Kim, Malle, Rouquier, et. al. on the cyclotomic Hecke algebras and their families of characters. ----- A un groupe de reflexions compl…
Let $X$ be a complete symmetric variety i.e. the wonderful compactification of a symmetric $G-$homogeneous space (where $G$ is a simply-connected semi-simple linear algebraic group). If $L$ is a line bundle over $X$ and if $C$ is a Bialynicki-Birula cell of codimension $c$ in $X$, then the Lie algebra $\mathfrak g$ of $G$ operates naturally on the cohomology group with support : $H^c_C(L)$. One gives here a necessary condition on the cell $C$ for that $\mathfrak g-$module have a finite dimensional simple subquotient. As applications one calculates the Euler-Poincaré characteristic of $L$ over …
We study the representation theory of three towers of algebras which are related to the symmetric groups and their Hecke algebras. The first one is constructed as the algebras generated simultaneously by the elementary transpositions and the elementary sorting operators acting on permutations. The two others are the monoid algebras of nondecreasing functions and nondecreasing parking functions. For these three towers, we describe the structure of simple and indecomposable projective modules, together with the Cartan map. The Grothendieck algebras and coalgebras given respectively by the induct…
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