Cartan-decomposition subgroups of SU(2,n)

A Cartan decomposition for non-symmetric reductive spherical pairs of rank-one type and its application to visible actions

A Cartan decomposition for symmetric pairs plays an important role to study not only orbit geometry of the symmetric spaces but also harmonic analysis on them. For non-symmetric reductive pairs, there are examples of generalizations of Cartan decompositions for some spherical complex homogeneous spaces such as complex line bundles over the complexified Hermitian symmetric spaces and triple spaces. This paper provides new examples of a Cartan decomposition for non-symmetric reductive pairs, namely, reductive non-symmetric spherical pairs of rank-one type. We also show that the action of some co…

Computation of the Cartan spaces of affine homogeneous spaces

Let $G$ be a reductive algebraic group and $H$ its reductive subgroup. Fix a Borel subgroup $B\subset G$ and a maximal torus $T\subset B$. The Cartan space $\a_{G,G/H}$ is, by definition, the subspace of $\Lie(T)^*$ generated by the weights of $B$-semiinvariant rational functions on $G/H$. We compute the spaces $\a_{G,G/H}$.

A branching law for subgroups fixed by an involution and a noncompact analogue of the Borel-Weil theorem

We give a branching law for subgroups fixed by an involution. As an application we give a generalization of the Cartan-Helgason theorem and a noncompact analogue of the Borel-Weil theorem.

Cartan decomposition of the moment map

We investigate a class of actions of real Lie groups on complex spaces. Using moment map techniques we establish the existence of a quotient and a version of Luna's slice theorem as well as a version of the Hilbert-Mumford criterion. A global slice theorem is proved for proper actions. We give new proofs of results of Mostow on decompositions of groups and homogeneous spaces.

Chip firing on Dynkin diagrams and McKay quivers

Two classes of avalanche-finite matrices and their critical groups (integer cokernels) are studied from the viewpoint of chip-firing/sandpile dynamics, namely, the Cartan matrices of finite root systems and the McKay-Cartan matrices for finite subgroups G of general linear groups. In the root system case, the recurrent and superstable configurations are identified explicitly and are related to minuscule dominant weights. In the McKay-Cartan case for finite subgroups of the special linear group, the cokernel is related to the abelianization of the subgroup G. In the special case of the classica…

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 …

Translation principle for Dirac index

Let $G$ be a finite cover of a closed connected transpose-stable subgroup of $GL(n,\bR)$ with complexified Lie algebra $\frg$. Let $K$ be a maximal compact subgroup of $G$, and assume that $G$ and $K$ have equal rank. We prove a translation principle for the Dirac index of virtual $(\frg,K)$-modules. As a byproduct, to each coherent family of such modules, we attach a polynomial on the dual of the compact Cartan subalgebra of $\frg$. This ``index polynomial'' generates an irreducible representation of the Weyl group contained in the coherent continuation representation. We show that the index …

A generalized Cartan decomposition for the double coset space U(n_1) x U(n_2) x U(n_3)) U(n) / U(p) x U(q)

Motivated by recent developments on visible actions on complex manifolds, we raise a question whether or not the multiplication of three subgroups $L$, $G'$ and $H$ surjects a Lie group $G$ in the setting that $G/H$ carries a complex structure and contains $G'/G' \cap H$ as a totally real submanifold. Particularly important cases are when $G/L$ and $G/H$ are generalized flag varieties, and we classify pairs of Levi subgroups $(L, H)$ such that $L G' H = G$, or equivalently, the real generalized flag variety $G'/H \cap G'$ meets every $L$-orbit on the complex generalized flag variety $G/H$ in t…

Weil 表示限制到开紧子群上的不可约分解

An irreducible decomposition of the Weil representation restricted to open compact subgroups

本文利用 Schrödinger 模型，对任意剩余特征的 p-进域，给出了 Weil 表示限制到极大开紧子群和 Iwahori 子群的不可约分解，并证明其无重数性。

Cartan型李超代数的抛物BGG范畴及其块分解

Parabolic BGG categories and their block decomposition for Lie superalgebras of Cartan type

本文研究复数域上Cartan型阶化李超代数的抛物BGG范畴，证明仅有极小和极大两类抛物子代数，并将问题简化为极小抛物范畴，进而证明射影覆盖存在性以建立块理论，最终完成块的分类及不可分解倾斜模与射影模的特征标公式计算。

McKay correspondence and the branching law for finite subgroups of $\mathbf{SL}_3\mathbb{C}$

Given $Γ$ a finite subgroup of $\mathbf{SL}_3\mathbb{C}$, we determine how an arbitrary finite dimensional irreducible representation of $\mathbf{SL}_3\mathbb{C}$ decomposes under the action of $Γ$. To the subgroup $Γ$ we attach a generalized Cartan matrix $C_Γ$. Then, inspired by B. Kostant, we decompose the Coxeter element of the Kac-Moody algebra attached to $C_Γ$ as a product of reflections of a special form, thereby suggesting an algebraic form for the McKay correspondence in dimension 3.

关于谢瓦莱群与根范畴IV的笔记：岩泽分解与全正性

Notes on Chevalley Groups and Root Category IV: Iwasawa Decomposition and Total Positivity

研究从根范畴探讨谢瓦莱群的嘉当和岩泽分解，以及其全正子幺半群的岩泽分解。

关于与Shalika子群相关的Bruhat分解

On a Bruhat decomposition related to the Shalika subgroup of $GL(2n)$

本文研究了与Shalika子群相关的GL(2n)群的双余类分解，并给出了其与Bruhat分解的联系。

Modular Invariants for Some Finite Pseudo-Reflection Groups

In this paper, we determine the modular invariants of finite modular pseudo-reflection subgroups of the finite general linear group $ \text{GL}_n(q) $ acting on the tensor product of the symmetric algebra $ S^{\bullet}(V) $ and the exterior algebra $ \wedge^{\bullet}(V) $ of the natural $ \text{GL}_n(q) $-module $ V $. We are particularly interested in the case where $ G $ is a subgroup of the parabolic subgroups of $ \text{GL}_n(q) $ which is a generalization of Weyl group of Cartan type Lie algebra.

Levi Subgroup Actions on Schubert Varieties, Induced Decompositions of their Coordinate Rings, and Sphericity Consequences

Let $L_w$ be the Levi part of the stabilizer $Q_w$ in $GL_N$ (for left multiplication) of a Schubert variety $X(w)$ in the Grassmannian $G_{d,N}$. For the natural action of $L_w$ on $\mathbb{C}[X(w)]$, the homogeneous coordinate ring of $X(w)$ (for the Plücker embedding), we give a combinatorial description of the decomposition of $\mathbb{C}[X(w)]$ into irreducible $L_w$-modules; in fact, our description holds more generally for the action of the Levi part $L$ of any parabolic subgroup $Q$ that is contained in $Q_w$. This decomposition is then used to show that all smooth Schubert varieties, …

对称子群作用下旗概形的一致分解

Uniform decomposition of the flag scheme by a symmetric subgroup action

该研究在局部常值假设下，建立了旗簇对称子群轨道分解经典结果的概形论版本，证明了轨道概形的仿射嵌入性，并通过经典例子给出相关概形论推论。

Decompositions of the stable module $\infty$-category

We show that the stable module $\infty$-category of a finite group $G$ decomposes in three different ways as a limit of the stable module $\infty$-categories of certain subgroups of $G$. Analogously to Dwyer's terminology for homology decompositions, we call these the centraliser, normaliser, and subgroup decompositions. We construct centraliser and normaliser decompositions and extend the subgroup decomposition (constructed by Mathew) to more collections of subgroups. The key step in the proof is extending the stable module $\infty$-category to be defined for any $G$-space, then showing that …