Total positivity in the De Concini-Procesi compactification

Representations of wreath products on cohomology of De Concini-Procesi compactifications

The wreath product W(r,n) of the cyclic group of order r and the symmetric group S_n acts on the corresponding projective hyperplane complement, and on its wonderful compactification as defined by De Concini and Procesi. We give a formula for the characters of the representations of W(r,n) on the cohomology groups of this compactification, extending the result of Ginzburg and Kapranov in the r=1 case. As a corollary, we get a formula for the Betti numbers which generalizes the result of Yuzvinsky in the r=2 case. Our method involves applying to the nested-set stratification a generalization of…

Rational cohomology of the real Coxeter toric variety of type A

The toric variety corresponding to the Coxeter fan of type A can also be described as a De Concini-Procesi wonderful model. Using a general result of Rains which relates cohomology of real De Concini-Procesi models to poset homology, we give formulas for the Betti numbers of the real toric variety, and the symmetric group representations on the rational cohomologies. We also show that the rational cohomology ring is not generated in degree 1.

Singular supports for character sheaves on a group compactification

Let $G$ be a semisimple adjoint group over $\bold C$ and $\bar{G}$ be the De Concini-Procesi completion of $G$. In this paper, we define a Lagrangian subvariety $Λ$ of the cotangent bundle of $\bar{G}$ such that the singular support of any character sheaf on $\bar{G}$ is contained in $Λ$.

Angle measures of some cones associated with finite reflection groups

We give a generalization of "Curious Identity" of De Concini and Procesi. Our proof is based on the recent result of Waldspurger about the decomposition of the cone dual to the fundamental chamber of a finite reflection group as a disjoint union of some subcones.

关于量子群的De Concini-Kac形式

On De Concini-Kac forms of quantum groups

本文提出偶部代数作为De Concini-Kac形式的修改，研究其在单位根顺序下的统一行为，并给出量子类比的Veldkamp定理。

Unipotent variety in the group compactification

The unipotent variety of a reductive algebraic group $G$ plays an important role in the representation theory. In this paper, we will consider the closure $\bar{\Cal U}$ of the unipotent variety in the De Concini-Procesi compactification $\bar{G}$ of a connected simple algebraic group $G$. We will prove that $\bar{\Cal U}-\Cal U$ is a union of some $G$-stable pieces introduced by Lusztig in \cite{L4}. This was first conjectured by Lusztig. We will also give an explicit description of $\bar{\Cal U}$. It turns out that similar results hold for the closure of any Steinberg fiber in $\bar{G}$.

Equation of some wonderful compactifications

De Concini and Procesi have defined the wonderful compactification of a symmetric space X=G/H with G a semisimple adjoint group and H the subgroup of fixed points of G by an involution s. It is a closed subvariety of a grassmannian of the Lie algebra L of G. In this paper, we prove that, when the rank of X is equal to the rank of G, the variety is defined by linear equations. The set of equations expresses the fact that the invariant alternate trilinear form w on L vanishes on the (-1)-eigenspace of s.

On small modules for quantum groups at roots of unity

A conjecture of De Concini Kac and Procesi provides a bound on the minimal possible dimension of an irreducible module for quantized enveloping algebras at an odd root of unity. We pose the problem of the existence of modules whose dimension equals this bound. We show that this question cannot have a positive answer in full generality and discuss variants of this question.

美妙紧化中的对角轨道

Diagonal orbits in the wonderful compactification

本文研究半单伴随群美妙紧化中的对角轨道，完成相关分类，通过单连通覆叠表示给出极大环面紧化的参数化，并构建Steinberg纤维闭包族证明其极限为He-Lusztig的G-稳定片并集。

半单李代数的Cartan子代数的奇妙紧化

Wonderful Compactification of a Cartan Subalgebra of a Semisimple Lie Algebra

本文定义了半单李代数Cartan子代数的紧化，证明其为法诺舒伯特簇，并研究了其边界除子、仿射铺砌、Weyl群作用及上同调环。