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arXiv 0904.3592math.DG
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具有齐次测地线的紧黎曼流形

Compact Riemannian Manifolds with Homogeneous Geodesics

D. V. Alekseevsky, Yu. G. Nikonorov

摘要:

齐次黎曼空间$(M= G/H,g)$称为测地线轨道空间(简称GO-空间),如果任何测地线是等距群$G$的单参数子群的轨道。研究了紧GO-空间的结构,给出了紧李群$G$的齐性空间上具有齐性测地线的不变度量$g$存在和不存在的充分条件.给出了具有正Euler特征的紧致单连通GO-空间$(M = G/H,g)$的一个分类.如果群$G$是单的,并且度量$g$不是来自$G$的双不变度量,则$M$是标志流形$M_1=SO(2n+1)/U(n)$或$M_2= Sp(n)/U(1)\cdot Sp(n-1)$之一,并且$g$是$M$上依赖于两个实参数的任何不变度量。在这两种情况下,存在唯一的(直到缩放)对称度量$g_0$,使得$(M,g_0)$分别是对称空间$M = SO(2n+2)/U(n+1)$或$\mathbb{C}P^{2n-1}$。流形$M_1$、$M_2$是弱对称空间。

英文摘要:

A homogeneous Riemannian space $(M= G/H,g)$ is called a geodesic orbit space (shortly, GO-space) if any geodesic is an orbit of one-parameter subgroup of the isometry group $G$. We study the structure of compact GO-spaces and give some sufficient conditions for existence and non-existence of an invariant metric $g$ with homogeneous geodesics on a homogeneous space of a compact Lie group $G$. We give a classification of compact simply connected GO-spaces $(M = G/H,g)$ of positive Euler characteristic. If the group $G$ is simple and the metric $g$ does not come from a bi-invariant metric of $G$, then $M$ is one of the flag manifolds $M_1=SO(2n+1)/U(n)$ or $M_2= Sp(n)/U(1)\cdot Sp(n-1)$ and $g$ is any invariant metric on $M$ which depends on two real parameters. In both cases, there exists unique (up to a scaling) symmetric metric $g_0$ such that $(M,g_0)$ is the symmetric space $M = SO(2n+2)/U(n+1)$ or, respectively, $\mathbb{C}P^{2n-1}$. The manifolds $M_1$, $M_2$ are weakly symmetric spaces.

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