Deformations of Adjoint orbits for semisimple Lie algebras and Lagrangian submanifolds

Complex adjoint orbits in Lie theory and geometry

This expository article is an introduction to the adjoint orbits of complex semisimple groups, primarily in the algebro-geometric and Lie-theoretic contexts, and with a pronounced emphasis on the properties of semisimple and nilpotent orbits. It is intended to build a foundation for more specialized settings in which adjoint orbits feature prominently (ex. hyperkähler geometry, Landau-Ginzburg models, and the theory of symplectic singularities). Also included are a few arguments and observations that, to the author's knowledge, have not yet appeared in the research literature.

Reducible spectral curves and the hyperkaehler geometry of adjoint orbits

We study the hyperkaehler geometry of a regular semisimple adjoint orbit of SL(k,C) via the algebraic geometry of the corresponding reducible spectral curve.

对称空间作为伴随轨道及其几何

Symmetric spaces as adjoint orbits and their geometries

本文通过将经典对称空间实现为对称旗流形的余切丛，研究其测地线与拉格朗日子流形，并首次构造出单连通流形上不能承载非负截面曲率度量的向量丛例子。

Slodowy slices and the complete integrability of Mishchenko-Fomenko subalgebras on regular adjoint orbits

This work is concerned with Mishchenko-Fomenko subalgebras and their restrictions to the adjoint orbits in a finite-dimensional complex semisimple Lie algebra. In this setting, it is known that each Mishchenko-Fomenko subalgebra restricts to a completely integrable system on every orbit in general position. We improve upon this result, showing that each Mishchenko-Fomenko subalgebra yields a completely integrable system on all regular orbits (i.e. orbits of maximal dimension). Our approach incorporates the theory of regular $\mathfrak{sl}_2$-triples and associated Slodowy slices, as developed …

超Kähler结构在超李泊利流形的叶上

Hyperkähler structures on leaves of hyper-Lie Poisson manifolds

本文探讨超Kähler结构在超李泊利流形叶上的两种不同构造方法的异同及联系。

Generalized Complex and Dirac Structures on Homogeneous Spaces

We partially describe equivariant Dirac and generalized complex structures on a homogeneous space $G/K$ by giving equivalent data involving only the Lie algebra. We consider real semisimple adjoint orbits in any semisimple Lie algebra over $\mathbb R$ and real nilpotent orbits in $sl_n (\mathbb R)$. We give a complete classification for Riemannian symmetric spaces and for a compact group modulo a closed, connected subgroup containing a Cartan subgroup.

Introduction to Lie groups, isometric and adjoint actions and some generalizations

The main purpose of these lecture notes is to provide a concise introduction to Lie groups, Lie algebras, and isometric and adjoint actions, aiming mostly at advanced undergraduate and graduate students. In addition, the connection between such classic theories and the research area of the first author is explored. Namely, generalizations to isoparametric submanifolds, polar actions and singular Riemannian foliations with sections (s.r.f.s.) are mentioned. The first chapters cover basic concepts, giving results on adjoint representation, closed subgroups, bi-invariant metrics, Killing forms an…

Growth Estimates for Orbits of Self Adjoint Groups

Let G denote a closed, connected, self adjoint, noncompact subgroup of GL(n,R), and let d_{R} denote the canonical right invariant Riemannian metric on G. For v in R^{n} let G_{v} = {g in G : g(v) = v}. We obtain algebraically defined upper and lower bounds for the asymptotic growth rate of g --> log |g(v)| / d_{R}(g,G_{v}), and these bounds are sharp if G_{v} is compact. If the lower bound is positive, then the orbit G(v) is closed in R^{n}. The results apply to representations of noncompact semisimple Lie groups G on finite dimensional real vector spaces.

Slices to sums of adjoint orbits, the Atiyah-Hitchin manifold, and Hilbert schemes of points

We show that the regular Slodowy slice to the sum of two semisimple adjoint orbits of $GL(n,C)$ is isomorphic to the deformation of the $D_2$-singularity if $n=2$, the Dancer deformation of the double cover of the Atiyah-Hitchin manifold if $n=3$, and to the Atiyah-Hitchin manifold itself if $n=4$. For higher $n$, such slices to the sum of two orbits, each having only two distinct eigenvalues, are either empty or biholomorphic to open subsets of the Hilbert scheme of points on of one the above surfaces. In particular, these open subsets of Hilbert schemes of points carry complete hyperkähler m…

Magnetic Flows on Homogeneous Spaces

We consider magnetic geodesic flows of the normal metrics on a class of homogeneous spaces, in particular (co)adjoint orbits of compact Lie groups. We give the proof of the non-commutative integrability of flows and show, in addition, for the case of (co)adjoint orbits, the usual Liouville integrability by means of analytic integrals. We also consider the potential systems on adjoint orbits, which are generalizations of the magnetic spherical pendulum. The complete integrability of such system is proved for an arbitrary adjoint orbit of a compact semisimple Lie group.

Normal holonomy of orbits and Veronese submanifolds

It was conjectured, twenty years ago, the following result that would generalize the so-called rank rigidity theorem for homogeneous Euclidean submanifolds: let M^n, n>=2, be a full and irreducible homogeneous submanifold of the sphere $S^{N-1}\subset R^N$ and such that the normal holonomy group is not transitive (on the unit sphere of the normal space to the sphere). Then M^n must be an orbit of an irreducible s-representation (i.e. the isotropy representation of a semisimple Riemannian symmetric space). If n=2, then the normal holonomy is always transitive, unless M is a homogeneous isoparam…

Generalizations of isoparametric foliations

Isoparametric submanifolds and hypersurfaces in space forms are geometric objects that have been studied since E. Cartan. Another important class of geometric objects is the orbits of a polar action on a Riemannian manifold,e.g., the orbits of the adjoint action of a Lie group on itself. These two classes of submanifolds share comon properties. For example, they are leaves of a singular Riemannian foliation with sections (s.r.f.s. for short). The purpose of this paper is to review some results of the theory of s.r.f.s., which have been developed by the author. In addition, we give an alternati…

Invariant hypercomplex structures and algebraic curves

We show that $U(k)$-invariant hypercomplex structures on (open subsets) of regular semisimple adjoint orbits in $\mathfrak{gl}(k,{\mathbb C})$ correspond to algebraic curves $C$ of genus $(k-1)^2$, equipped with a flat projection $π:C\to{\mathbb P}^1$ of degree $k$, and an antiholomorphic involution $σ:C\to C$ covering the antipodal map on ${\mathbb P}^1$.

广义双括号向量场

Generalized double bracket vector fields

本文提出广义双括号向量场，将其推广至带伪黎曼度量的泊松流形，并用于哈密顿系统的平衡点渐近稳定化。

Combinatorics of Vogan diagrams for almost-Kähler manifolds

Let $G$ be a non-compact classical semisimple Lie group and let $G/V$ be the adjoint orbit with respect to a fixed element in $G$. These manifolds can be equipped with an almost-Kähler structure and we provide explicit formulae for the existence of special almost-complex structures on $G/V$ purely in terms of the combinatorics of the associated Vogan diagram. The formulae are given separately for Lie groups whose Lie algebras are of type $A_{\ell}$, $B_{\ell}$, $C_{\ell}$, $D_{\ell}$, where $\ell$ denotes the rank of the Lie algebra.

Invariant Einstein metrics on generalized flag manifolds with two isotropy summands

Let $M=G/K$ be a generalized flag manifold, that is the adjoint orbit of a compact semisimple Lie group $G$. We use the variational approach to find invariant Einstein metrics for all flag manifolds with two isotropy summands. We also determine the nature of these Einstein metrics as critical points of the scalar curvature functional under fixed volume.

接触化副Kähler流形上的不变Monge-Ampère方程

Invariant Monge-Ampère equations on contactified para-Kähler manifolds

提出一种描述半单李群齐性接触流形上不变Monge-Ampère方程的方法，并将其应用于例外李群$\mathsf{G}_2$的十维轨道，得出了完整的相互不等价MAE列表。

Embeddings of semisimple complex Lie groups and cohomological components of modules

Let G --> G' be an embedding of semisimple complex Lie groups, let B and B' be a pair of nested Borel subgroups, and let f:G/B --> G'/B' be the associated equivariant embedding of flag manifolds. We study the pullbacks of cohomologies of invertible sheaves on G'/B' along the embedding f. Let O' be a G'-equivariant invertible sheaf on G'/B', and let O be its restriction to G/B. Consider the G-equivariant pullback on cohomology p : H(G'/B',O') --> H(G/B,O). The Borel-Weil-Bott theorem implies that the two cohomology spaces above are irreducible modules of G' and G respectively. By Schur's lemma,…

无限维量子动力学的几何结构

Geometry of quantum dynamics in infinite dimension

本研究基于Tulczyjew三元组构建无限维量子力学几何方法，将自伴算子对应为拉格朗日子流形，同时得到酉群余伴随轨道、希尔伯特射影空间嵌入及对称关系自伴延拓的相关成果。

On a class of geodesic orbit spaces with abelian isotropy subgroup

Riemannian geodesic orbit spaces (G/H,g) are natural generalizations of symmetric spaces, defined by the property that their geodesics are orbits of one-parameter subgroups of G. We study the geodesic orbit spaces of the form (G/S,g), where G is a compact, connected, semisimple Lie group and S is abelian. We give a simple geometric characterization of those spaces, namely that they are naturally reductive. In turn, this yields the classification of the invariant geodesic orbit (and also the naturally reductive) metrics on any space of the form G/S. Our approach involves simplifying the intrica…