关于Dirac结构

本文给出了Dirac流形几何化的刻画;证明了Poisson流形上的Dirac结构是Courant最初定义的Dirac结构通过扭曲得到的.     

利用Dirac理论进行Poisson流形及Jacobi流形的约化(英文)

通过将可约的Dirac以及Jacobi-Dirac结构分别分为两种类型,给出对应于Poisson流形和Jacobi流形的约化定理.这些约化定理的证明只需要进行一些直接的计算,而不需要借助于矩映射或者相容函数等复杂概念的引入.另外,给出了一些相应的例子和应用.     

关于Dirac结构

本文给出了 Ｄｉｒａｃ流形几何化的刻画;证明了 Ｐｏｉｓｓｏｎ流形上的Ｄｉｒａｃ结构是Ｃｏｕｒａｎｔ最初定义的 Ｄｉｒａｃ结构通过扭曲得到的．     

约化Poisson作用

给出了Poisson Lie商群作用于Poisson商流形成为Poisson作用的充要条件 ,其中 ,商群和商流形的Poisson结构都由Dirac结构诱导 .建立了Poisson齐性空间的左不变Dirac结构与左不变张量两种刻画的等价关系 .     

Poisson系统的辛结构

当Poisson系统中的Poisson矩阵是非常数时,经典的辛方法如辛Runge-Kutta方法,生成函数法一般不能保持Poisson系统的Poisson结构,利用非线性变换可把非常数Poisson结构转化成辛结构,然后任意阶的辛方法可以长时间计算Poisson系统的辛结构．自由刚体问题中Euler方程被转换成辛结构并用辛中点格式进行数值求解,数值结果给出了这种非线性变换的有效性．     

切Poisson作用及约化

本文证明了单连通Poisson紧李群切作用及约化Poisson作用于Poisson流形，若带有等动量映射，则可通过调整Poisson流形的Poisson结构，变成保Poisson结构的Poisson作用，并且该作用限制到Poisson流形的辛叶片上，相对于新Poisson结构是Hamiltion作用。我们把Meyer-Marsden-Weinstein约化从Hamiltion作用推广到切Poisson作用，包括正则值和非正则值两种形式。     

局部对称Bochner-Kaehler流形及其Kaehler子流形

本文给出局部对称的Bochner-Kaehler流形的Riemann结构以及它的Kaehler子流形为全测地子流形的几个Pinching条件,推广了关于复射影空间的Kaehler子流形的相应定理。     

局部对称共形平坦黎曼流形中的紧致子流形

本文讨论局部对称共形平坦黎曼流形中紧子流形问题．改进了［１］的结果并将［２］中关于球面子流形的一个结果推广到局部对称共形平坦黎曼流形子流形．     

一个Maslov指标公式及应用

本文给出辛流形（Ｍ，ω）和（Ｍ，－ω）的乘积辛流形（Ｍ×Ｍ，ω⊕（－ω））中Ｌａ－ｇｒａｎｇｅ子流形ΔＭ：＝｛（ｘ，ｘ）｜ｘ∈Ｍ）的Ｍａｓｌｏｖ指标的计算公式，并讨论它的一些应用．     

3-流形上的Poisson矩阵及其应用

本文利用可定向3-流形切丛的平凡性,在3维几何上建立了一种整体标架法.对于3-流形上任一整体切标架,定义了一个Poisson矩阵,并给出:Poisson矩阵在标架改变时的变化规律.以Poisson矩阵为原始数据,计算了相应Riemannian度量各种曲率的具体表达式.对于具有常值Poisson矩阵的一类3-流形,这个方法被用来讨论它们的拓扑结构.它们基本上都是3维李群在其离散子群左平移作用下的商空间.     

Induced Dirac structures on isotropy-type manifolds

A new method of singular reduction is extended from Poisson to Dirac manifolds. Then it is shown that the Dirac structures on the strata of the quotient coincide with those of the only other known singular Dirac reduction method.     

Dirac submanifolds and Poisson involutions

Dirac submanifolds are a natural generalization in the Poisson category of the symplectic submanifolds of a symplectic manifold. They correspond to symplectic subgroupoids of the symplectic groupoid of the given Poisson manifold. In particular, Dirac submanifolds arise as the stable loci of Poisson involutions. In this paper, we make a general study of these submanifolds including both local and global aspects.In the second part of the paper, we study Poisson involutions and the induced Poisson structures on their stable loci. In particular, we discuss the Poisson involutions on a special class of Poisson groups, and more generally Poisson groupoids, called symmetric Poisson groups, and symmetric Poisson groupoids. Many well-known examples, including the standard Poisson group structures on semi-simple Lie groups, Bruhat Poisson structures on compact semi-simple Lie groups, and Poisson groupoid structures arising from dynamical r-matrices of semi-simple Lie algebras are symmetric, so they admit a Poisson involution. For symmetric Poisson groups, the relation between the stable locus Poisson structure and Poisson symmetric spaces is discussed. As a consequence, we prove that the Dubrovin Poisson structure on the space of Stokes matrices U₊ (appearing in Dubrovin's theory of Frobenius manifolds) is a Poisson symmetric space.     

Reduction of Jacobi manifolds via Dirac structures theory

We first recall some basic definitions and facts about Jacobi manifolds, generalized Lie bialgebroids, generalized Courant algebroids and Dirac structures. We establish an one-one correspondence between reducible Dirac structures of the generalized Lie bialgebroid of a Jacobi manifold (M,Λ,E) for which 1 is an admissible function and Jacobi quotient manifolds of M. We study Jacobi reductions from the point of view of Dirac structures theory and we present some examples and applications.     

群胚上的Dirac结构及泊松约化

本文详细讨论了李双代数胚中的Dirac结构、群胚上的Dirac结构。利用Dirac结构的特征对的概念,给出了作用不变Dirac结构,拉回Dirac结构等概念的新的刻画。最后利用Dirac结构的有关性质,讨论了泊松齐性空间和泊松群胚作用的约化。     

Dirac structures and their composition on Hilbert spaces

Dirac structures appear naturally in the study of certain classes of physical models described by partial differential equations and they can be regarded as the underlying power conserving structures. We study these structures and their properties from an operator-theoretic point of view. In particular, we find necessary and sufficient conditions for the composition of two Dirac structures to be a Dirac structure and we show that they can be seen as Lagrangian (hyper-maximal neutral) subspaces of Kre?n spaces. Moreover, special emphasis is laid on Dirac structures associated with operator colligations. It turns out that this class of Dirac structures is linked to boundary triplets and that this class is closed under composition.     

Multiplicative Dirac structures on Lie groups

We study multiplicative Dirac structures on Lie groups. We show that the characteristic foliation of a multiplicative Dirac structure is given by the cosets of a normal Lie subgroup and, whenever this subgroup is closed, the leaf space inherits the structure of a Poisson–Lie group. We also describe multiplicative Dirac structures on Lie groups infinitesimally. To cite this article: C. Ortiz, C. R. Acad. Sci. Paris, Ser. I 346 (2008).     

The Dirac Operator on Nilmanifolds and Collapsing Circle Bundles

We compute the spectrum of the Dirac operator on 3-dimensional Heisenberg manifolds. The behavior under collapse to the 2-torus is studied. Depending on the spin structure either all eigenvalues tend to ± or there are eigenvalues converging to those of the torus. This is shown to be true in general for collapsing circle bundles with totally geodesic fibers. Using the Hopf fibration we use this fact to compute the Dirac eigenvalues on complex projective space including the multiplicities.Finally, we show that there are 1-parameter families of Riemannian nilmanifolds such that the Laplacian on functions and the Dirac operator for certain spin structures have constant spectrum while the Laplacian on 1-forms and the Dirac operator for the other spin structures have nonconstant spectrum. The marked length spectrum is also constant for these families.     

Dirac structures and paracomplex manifolds

We introduce the notion of a generalized paracomplex structure. This is a natural notion which unifies several geometric structures such as symplectic forms, paracomplex structures, and Poisson structures. We show that generalized paracomplex structures are in one-to-one correspondence with pairs of transversal Dirac structures on a smooth manifold. To cite this article: A. Wade, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Geometric connections and geometric Dirac operators on contact manifolds

We construct some natural metric connections on metric contact manifolds compatible with the contact structure and characterized by the Dirac operators they determine. In the case of CR manifolds these are invariants of a fixed pseudo-hermitian structure, and one of them coincides with the Tanaka-Webster connection.