K-area, Hofer metric and geometry of conjugacy classes in Lie groups

Hofer geometry and cotangent fibers

For a class of Riemannian manifolds that include products of arbitrary compact manifolds with manifolds of nonpositive sectional curvature on the one hand, or with certain positive-curvature examples such as spheres of dimension at least 3 and compact semisimple Lie groups on the other, we show that the Hamiltonian diffeomorphism group of the cotangent bundle contains as subgroups infinite-dimensional normed vector spaces that are bi-Lipschitz embedded with respect to Hofer's metric; moreover these subgroups can be taken to consist of diffeomorphisms supported in an arbitrary neighborhood of t…

Hofer几何领域中的辛积分器

Symplectic integrators in the realm of Hofer's geometry

研究从哈密顿和李形式构造的辛积分器，利用Hofer几何优化不同辛格式的耦合，得到Parareal方法中哈密顿动力学良好行为的约束。

随机哈密顿量 II：中心极限定理与随机游走的霍弗几何

Random Hamiltonians II: A central limit theorem and the Hofer geometry of random walks

本文利用随机游走研究哈密顿微分同胚群的整体几何，证明其随机游走期望霍弗范数增长与步数平方根相关，给出相关测度、可测性及中心极限定理的结果。

Sums of Adjoint Orbits

Let G be a real compact connected simple Lie group, and g its Lie algebra. We study the problem of determining, from root data, when a sum of adjoint orbits in g, or a product of conjugacy classes in G, contains an open set. Our general methods allow us to determine exactly which sums of adjoint orbits in su(m) and products of conjugacy classes in SU(m) contain an open set, in terms of the highest multiplicities of eigenvalues. For su(m) and SU(m) we show L^2--singular dichotomy: The convolution of invariant measures on adjoint orbits, or conjugacy classes, is either singular to Haar measure o…

Maximal Tori in Contactomorphism Groups

I describe a general scheme which associates conjugacy classes of tori in the contactomorphism group to transverse almost complex structures on a compact contact manifold. Moreover, to tori of Reeb type whose Lie algebra contains a Reeb vector field one can associate a Sasaki cone. Thus, for contact structures of K-contact type one obtains a configuration of Sasaki cones called a bouquet such that each Sasaki cone is associated with a conjugacy class of tori of Reeb type.

Pure Spinors on Lie groups

For any manifold M, the direct sum TM \oplus T*M carries a natural inner product given by the pairing of vectors and covectors. Differential forms on M may be viewed as spinors for the corresponding Clifford bundle, and in particular there is a notion of \emph{pure spinor}. In this paper, we study pure spinors and Dirac structures in the case when M=G is a Lie group with a bi-invariant pseudo-Riemannian metric, e.g. G semi-simple. The applications of our theory include the construction of distinguished volume forms on conjugacy classes in G, and a new approach to the theory of quasi-Hamiltonia…

On the $T$-leaves and the ranks of a Poisson structure on twisted conjugacy classes

Let $G$ be a connected complex semisimple Lie group with a fixed maximal torus $T$ and a Borel subgroup $B \supset T$. For an arbitrary automorphism $θ$ of $G$, we introduce a holomorphic Poisson structure $π_θ$ on $G$ which is invariant under the $θ$-twisted conjugation by $T$ and has the property that every $θ$-twisted conjugacy class of $G$ is a Poisson subvariety with respect to $π_θ$. We describe the $T$-orbits of symplectic leaves, called $T$-leaves, of $π_θ$ and compute the dimensions of the symplectic leaves (i.e, the ranks) of $π_θ$. We give the lowest rank of $π_θ$ in any given $θ$-t…

Group systems, groupoids, and moduli spaces of parabolic bundles

Let $G$ be a Lie group, with an invariant non-degenerate symmetric bilinear form on its Lie algebra, let $π$ be the fundamental group of an orientable (real) surface $M$ with a finite number of punctures, and let $\bold C$ be a family of conjugacy classes in $G$, one for each puncture. A finite-dimensional construction used earlier to obtain a symplectic structure on the moduli space of flat $G$-bundles over compact $M$ is extended to the punctured case. It yields a symplectic structure on a certain smooth manifold $\Cal M_{\bold C}$ containing the space $\roman{Hom}(π,G)_{\bold C}$ of homomor…

Higher algebraic structures in Hamiltonian Floer theory I

This is the first of two papers devoted to showing how the rich algebraic formalism of Eliashberg-Givental-Hofer's symplectic field theory (SFT) can be used to define higher algebraic structures on the symplectic cohomology of open symplectic manifolds. Using the SFT of Hamiltonian mapping tori we show how to define a homotopy extension of the well-known Lie bracket on symplectic cohomology. Apart from discussing applications to the existence of closed Reeb orbits, we outline how the $L_{\infty}$-structure is conjecturally related via mirror symmetry to the extended deformation theory of compl…

Higher algebraic structures in Hamiltonian Floer theory

In this paper we show how the rich algebraic formalism of Eliashberg-Givental-Hofer's symplectic field theory (SFT) can be used to define higher algebraic structures in Hamiltonian Floer theory. Using the SFT of Hamiltonian mapping tori we show how to define a homotopy extension of the well-known Lie bracket and discuss how it can be used to prove the existence of multiple closed Reeb orbits. Furthermore we show how to define the analogue of rational Gromov-Witten theory in the Hamiltonian Floer theory of open symplectic manifolds. More precisely, we introduce a so-called cohomology F-manifold…