共查询到20条相似文献,搜索用时 0 毫秒
1.
Geometriae Dedicata - We show a kind of Obata-type theorem on a compact Einstein n-manifold $$(W, bar{g})$$ with smooth boundary $$partial W$$ . Assume that the boundary $$partial W$$ is minimal... 相似文献
2.
3.
4.
5.
6.
In this paper we establish the best constants for a Sobolev inequality and a Sobolev trace inequality on compact Riemannian manifolds with boundary, the functions being invariant under the action of a compact subgroup G of the isometry group I(M,g) and we give applications to some nonlinear PDEs with upper critical Sobolev exponent. 相似文献
7.
Radu Pantilie John C. Wood 《Transactions of the American Mathematical Society》2002,354(10):4229-4243
We prove that, from an Einstein manifold of dimension greater than or equal to five, there are just two types of harmonic morphism with one-dimensional fibres. This generalizes a result of R.L. Bryant who obtained the same conclusion under the assumption that the domain has constant curvature.
8.
Jaeman Kim 《Monatshefte für Mathematik》2007,152(3):251-254
We show that every compact Einstein Hermitian surface with constant *–scalar curvature is a K?hler surface. In contrast to
the 4-dimensional case, it is shown that there exists a compact Einstein Hermitian (4n + 2)-dimensional manifold with constant *–scalar curvature which is not K?hler.
This study is supported by Kangwon National University. 相似文献
9.
In this paper we give some examples of a quasi Einstein manifold (QE)n. Next we prove the existence of (QE)n manifolds. Then we study some properties of a quasi Einstein manifold. Finally the hypersurfaces of a Euclidean space have been studied. 相似文献
10.
Jaeman Kim 《Monatshefte für Mathematik》2007,47(1):251-254
We show that every compact Einstein Hermitian surface with constant *–scalar curvature is a K?hler surface. In contrast to
the 4-dimensional case, it is shown that there exists a compact Einstein Hermitian (4n + 2)-dimensional manifold with constant *–scalar curvature which is not K?hler. 相似文献
11.
Christoph Bö hm Megan M. Kerr 《Transactions of the American Mathematical Society》2006,358(4):1455-1468
We show that compact, simply connected homogeneous spaces up to dimension admit homogeneous Einstein metrics.
12.
13.
Hassan Akbar-Zadeh 《Comptes Rendus Mathematique》2004,339(2):125-130
A formula linking the horizontal Laplacian of a function φ on the fibre bundle W of unitary tangent vectors to a Finslerian compact manifold without boundary , to the square of a symmetric 2-tensor and Finslerian curvature. From it an estimate, under a certain condition, is obtained for the function . If where k is a positive constant and M simply connected, then M is homeomorphic to an n-sphere. Let be a deformation of preserving the volume of W. One proves that the critical points of the integral of a certain Finslerian scalar curvature on W define a generalized Einstein manifold. One calculates the second variationals at the critical points first in the general case, then, for an infinitesimal conformal deformation and one shows that in certain cases one has . We also study the case when the scalar curvature is non-positive constant. To cite this article: H. Akbar-Zadeh, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献
14.
We prove that if $M^n(n\ge 4)$ is a compact Einstein manifold whose normalized scalar curvature and sectional curvature satisfy pinching condition $R_0>\sigma _{n}K_{\max }$ , where $\sigma _n\in (\frac{1}{4},1)$ is an explicit positive constant depending only on $n$ , then $M$ must be isometric to a spherical space form. Moreover, we prove that if an $n(\ge {\!\!4})$ -dimensional compact Einstein manifold satisfies $K_{\min }\ge \eta _n R_0,$ where $\eta _n\in (\frac{1}{4},1)$ is an explicit positive constant, then $M$ is locally symmetric. It should be emphasized that the pinching constant $\eta _n$ is optimal when $n$ is even. We then obtain some rigidity theorems for Einstein manifolds under $(n-2)$ -th Ricci curvature and normalized scalar curvature pinching conditions. Finally we extend the theorems above to Einstein submanifolds in a Riemannian manifold, and prove that if $M$ is an $n(\ge {\!\!4})$ -dimensional compact Einstein submanifold in the simply connected space form $F^{N}(c)$ with constant curvature $c\ge 0$ , and the normalized scalar curvature $R_0$ of $M$ satisfies $R_0>\frac{A_n}{A_n+4n-8}(c+H^2),$ where $A_n=n^3-5n^2+8n$ , and $H$ is the mean curvature of $M$ , then $M$ is isometric to a standard $n$ -sphere. 相似文献
15.
Jeremy Wong 《Geometriae Dedicata》2010,149(1):291-334
This paper studies manifolds-with-boundary collapsing in the Gromov– Hausdorff topology. The main aim is an understanding of the relationship of the topology and geometry of a limiting sequence of manifolds-with-boundary to that of a limit space, which is presumed to be without geodesic terminals. The first group of results provide a fiber bundle structure to the manifolds-with-boundary. One of the main theorems establishes a disc bundle structure for any manifold-with-boundary having two-sided bounds on sectional curvature and second fundamental form, and a lower bound on intrinsic injectivity radius, which is sufficiently close in the Gromov–Hausdorff topology to a closed manifold. Another result is a rough version of Toponogov’s Splitting Theorem. The second group of results identify Gromov–Hausdorff limits of certain sequences of manifolds with non-convex boundaries as Alexandrov spaces of curvature bounded below. 相似文献
16.
17.
Daniel Guan 《Transactions of the American Mathematical Society》2005,357(8):3359-3373
In this note we give a structure theorem for a finite-dimensional subgroup of the automorphism group of a compact symplectic manifold. An application of this result is a simpler and more transparent proof of the classification of compact homogeneous spaces with invariant symplectic structures. We also give another proof of the classification from the general theory of compact homogeneous spaces which leads us to a splitting conjecture on compact homogeneous spaces with symplectic structures (which are not necessary invariant under the group action) that makes the classification of this kind of manifold possible.
18.
By making use of the symplectic reduction and the cohomogeneity method, we give a general method for constructing Hamiltonian minimal Lagrangian submanifolds in Kaehler manifolds with symmetries. As applications, we construct infinitely many nontrivial complete Hamiltonian minimal Lagrangian submanifolds in CPn and Cn. 相似文献
19.
Summary At first, a necessary and sufficient condition for a K?hler-Norden manifold to be holomorphic Einstein is found. Next, it
is shown that the so-called (real) generalized Einstein conditions for K?hler-Norden manifolds are not essential since the
scalarcurvature of such manifolds is constant. In this context, we study generalized holomorphic Einstein conditions. Using
the one-to-one correspondence between K?hler-Norden structures and holomorphic Riemannian metrics, we establish necessary
and sufficient conditions for K?hler-Norden manifolds to satisfy the generalized holomorphic Einstein conditions. And a class
of new examples of such manifolds is presented. Finally, in virtue of the obtained results, we mention that Theorems 1 and
2 of H. Kim and J. Kim [10] are not true in general. 相似文献
20.
Charles P. Boyer Krzysztof Galicki 《Proceedings of the American Mathematical Society》2001,129(8):2419-2430
We show that every K-contact Einstein manifold is Sasakian-Einstein and discuss several corollaries of this result.