Expand all Collapse all  Results 51  75 of 82 
51. CMB 2007 (vol 50 pp. 24)
Invariant Metrics with Nonnegative Curvature on Compact Lie Groups We classify the leftinvariant metrics with nonnegative sectional curvature on $\SO(3)$ and $U(2)$.
Category:53C20 
52. CMB 2006 (vol 49 pp. 321)
Polygons with Prescribed Gauss Map in Hadamard Spaces and Euclidean Buildings We show that given a stable weighted configuration on the asymptotic
boundary of a
locally compact Hadamard space, there is a polygon with Gauss
map prescribed by the given weighted configuration.
Moreover, the same result holds for
semistable configurations on arbitrary Euclidean buildings.
Keywords:Euclidean buildings, Hadamard spaces, polygons Category:53C20 
53. CMB 2006 (vol 49 pp. 226)
The Spectrum and Isometric Embeddings of Surfaces of Revolution A sharp upper bound on the first $S^{1}$ invariant eigenvalue of the Laplacian
for $S^1$ invariant metrics on $S^2$ is used to find obstructions to the existence
of $S^1$ equivariant isometric embeddings of such metrics in $(\R^3,\can)$. As a
corollary we prove: If the first four distinct eigenvalues have even multiplicities
then the metric cannot be equivariantly, isometrically embedded in $(\R^3,\can)$. This
leads to generalizations of some classical results in the theory of surfaces.
Categories:58J50, 58J53, 53C20, 35P15 
54. CMB 2006 (vol 49 pp. 134)
Real Hypersurfaces in Complex TwoPlane Grassmannians with Vanishing Lie Derivative In this paper we give a characterization of real hypersurfaces of type $A$ in a complex
twoplane Grassmannian $G_2(\mathbb{C}^{m+2})$ which are tubes over totally geodesic
$G_2(\mathbb{C}^{m+1})$ in $G_2(\mathbb{C}^{m+2})$ in terms of the {\it vanishing Lie
derivative\/} of the shape operator $A$ along the direction of the Reeb vector field $\xi$.
Categories:53C40, 53C15 
55. CMB 2006 (vol 49 pp. 152)
Comparison Geometry With\\$L^1$Norms of Ricci Curvature We investigate the geometry of manifolds with bounded Ricci
curvature in $L^1$sense. In particular, we generalize the
classical volume comparison theorem to our situation and obtain a
generalized sphere theorem.
Keywords:Mean curvature, Ricci curvature Category:53C20 
56. CMB 2006 (vol 49 pp. 36)
Holomorphic Frames for Weakly Converging Holomorphic Vector Bundles Using a modification of Webster's proof of the NewlanderNirenberg
theorem, it is shown that, for a weakly convergent sequence of
integrable unitary connections on a complex vector bundle over a
complex manifold, there is a subsequence of local holomorphic frames
that converges strongly in an appropriate Holder class.
Categories:57M50, 58E20, 53C24 
57. CMB 2005 (vol 48 pp. 561)
A Note on Lagrangian Loci of Quotients We study Hamiltonian actions of compact groups in the presence of
compatible involutions. We show that the Lagrangian fixed point set
on the symplectically reduced space is isomorphic to the disjoint
union of the involutively reduced spaces corresponding to
involutions on the group strongly inner to the given one.
Our techniques imply that the solution to the eigenvalues of a sum problem
for a given real form can be reduced to the quasisplit real form in the
same inner class. We also consider invariant quotients with respect to
the corresponding real form of the complexified group.
Keywords:Quotients, involutions, real forms, Lagrangian loci Category:53D20 
58. CMB 2005 (vol 48 pp. 112)
On Negatively Curved Finsler Manifolds of Scalar Curvature In this paper, we prove a global rigidity theorem for negatively
curved Finsler metrics on a compact manifold of dimension $n \geq 3$.
We show that for such a Finsler manifold, if the flag curvature is a
scalar function on the tangent bundle, then the Finsler metric is of
Randers type. We also study the case when the Finsler metric is
locally projectively flat
Category:53C60 
59. CMB 2004 (vol 47 pp. 624)
A Compactness Theorem for YangMills Connections In this paper, we consider YangMills connections
on a vector bundle $E$ over a compact Riemannian manifold $M$ of
dimension $m> 4$, and we show that any set of YangMills
connections with the uniformly bounded $L^{\frac{m}{2}}$norm of
curvature is compact in $C^{\infty}$ topology.
Keywords:YangMills connection, vector bundle, gauge transformation Categories:58E20, 53C21 
60. CMB 2004 (vol 47 pp. 492)
Isotropic Immersions with Low Codimension of Complex Space Forms into Real Space Forms The main purpose of this paper is to determine
isotropic immersions of complex
space forms into real space forms with low
codimension. This is an improvement of a result of S. Maeda.
Categories:53B25, 53C235 
61. CMB 2004 (vol 47 pp. 354)
An Integral Formula on Seifert Bundles We prove an integral formula on closed oriented
manifolds equipped with a codimension two foliation whose leaves
are compact.
Categories:53C12, 53C15. 
62. CMB 2004 (vol 47 pp. 314)
Mean Curvature Comparison with $L^1$norms of Ricci Curvature We prove an analogue of mean curvature comparison theorem in the case where the
Ricci curvature below a positive constant is small in $L^1$norm.
Keywords:mean curvature, Ricci curvature Category:53C20 
63. CMB 2003 (vol 46 pp. 617)
On Harmonic Theory in Flows Recently [8], a harmonic theory was developed for a compact
contact manifold from the viewpoint of the transversal geometry of
contact flow. A contact flow is a typical example of geodesible
flow. As a natural generalization of the contact flow, the present
paper develops a harmonic theory for various flows on compact
manifolds. We introduce the notions of $H$harmonic and
$H^*$harmonic spaces associated to a H\"ormander flow. We also
introduce the notions of basic harmonic spaces associated to a weak
basic flow. One of our main results is to show that in the special
case of isometric flow these harmonic spaces are isomorphic to the
cohomology spaces of certain complexes. Moreover, we find an
obstruction for a geodesible flow to be isometric.
Keywords:contact structure, geodesible flow, isometric flow, basic cohomology Categories:53C20, 57R30 
64. CMB 2003 (vol 46 pp. 277)
Rigidity of Hamiltonian Actions This paper studies the following question: Given an
$\omega'$symplectic action of a Lie group on a manifold $M$ which
coincides, as a smooth action, with a Hamiltonian $\omega$action,
when is this action a Hamiltonian $\omega'$action? Using a result of
MorseBott theory presented in Section~2, we show in Section~3 of this
paper that such an action is in fact a Hamiltonian $\omega'$action,
provided that $M$ is compact and that the Lie group is compact and
connected. This result was first proved by LalondeMcDuffPolterovich
in 1999 as a consequence of a more general theory that made use of
hard geometric analysis. In this paper, we prove it using classical
methods only.
Categories:53D05, 37J25 
65. CMB 2003 (vol 46 pp. 130)
On Frankel's Theorem In this paper we show that two minimal hypersurfaces in a manifold with
positive Ricci curvature must intersect. This is then generalized to show
that in manifolds with positive Ricci curvature in the integral sense two
minimal hypersurfaces must be close to each other. We also show
what happens if a manifold with nonnegative Ricci curvature admits
two nonintersecting minimal hypersurfaces.
Keywords:Frankel's Theorem Category:53C20 
66. CMB 2002 (vol 45 pp. 378)
The Local MÃ¶bius Equation and Decomposition Theorems in Riemannian Geometry A partial differential equation, the local M\"obius equation, is
introduced in Riemannian geometry which completely characterizes the
local twisted product structure of a Riemannian manifold. Also the
characterizations of warped product and product structures of
Riemannian manifolds are made by the local M\"obius equation and an
additional partial differential equation.
Keywords:submersion, MÃ¶bius equation, twisted product, warped product, product Riemannian manifolds Categories:53C12, 58J99 
67. CMB 2002 (vol 45 pp. 161)
Sur les singularitÃ©s de la fonction croissance d'une variÃ©tÃ© non simplement connexe Si $M$ est une vari\'et\'e de dimension $n$, compacte non simplement
connexe, on caract\'erise les m\'etriques riemanniennes sur $M$ dont
la fonction croissance a exactement deux singularit\'es.
Keywords:fonction croissance, singularitÃ©s, fonction de Morse, Cutlocus Category:53B20 
68. CMB 2002 (vol 45 pp. 232)
On Strongly Convex Indicatrices in Minkowski Geometry The geometry of indicatrices is the foundation of Minkowski geometry.
A strongly convex indicatrix in a vector space is a strongly convex
hypersurface. It admits a Riemannian metric and has a distinguished
invariant(Cartan) torsion. We prove the existence of nontrivial
strongly convex indicatrices with vanishing mean torsion and discuss
the relationship between the mean torsion and the Riemannian curvature
tensor for indicatrices of Randers type.
Categories:46B20, 53C21, 53A55, 52A20, 53B40, 53A35 
69. CMB 2001 (vol 44 pp. 408)
Finite Groups Generated by Involutions on Lagrangian Planes of $\mathbf{C}^2$ We classify finite subgroups of $\SO(4)$ generated by antiunitary
involutions. They correspond to involutions fixing pointwise a
Lagrangian plane. Explicit descriptions of the finite groups and the
configurations of Lagrangian planes are obtained.
Categories:22E40, 53D99 
70. CMB 2001 (vol 44 pp. 376)
A Note on $p$Harmonic $1$Forms on Complete Manifolds In this paper we prove that there is no nontrivial $L^{q}$integrably
$p$harmonic $1$form on a complete manifold with nonnegatively Ricci
curvature $(0

71. CMB 2001 (vol 44 pp. 129)
LinÃ©arisation symplectique en dimension 2 In this paper the germ of neighborhood of a compact leaf in a
Lagrangian foliation is symplectically classified when the compact
leaf is $\bT^2$, the affine structure induced by the Lagrangian
foliation on the leaf is complete, and the holonomy of $\bT^2$ in
the foliation linearizes. The germ of neighborhood is classified by a
function, depending on one transverse coordinate, this function is
related to the affine structure of the nearly compact leaves.
Keywords:symplectic manifold, Lagrangian foliation, affine connection Categories:53C12, 58F05 
72. CMB 2001 (vol 44 pp. 70)
The Tangent Bundle of an Almost Complex Manifold Motivated by deformation theory of holomorphic maps between almost
complex manifolds we endow, in a natural way, the tangent bundle of
an almost complex manifold with an almost complex structure. We
describe various properties of this structure.
Category:53C15 
73. CMB 2001 (vol 44 pp. 36)
Quantization of Bending Deformations of Polygons In $\mathbb{E}^3$, Hypergeometric Integrals and the Gassner Representation 
Quantization of Bending Deformations of Polygons In $\mathbb{E}^3$, Hypergeometric Integrals and the Gassner Representation The Hamiltonian potentials of the bending deformations of $n$gons
in $\E^3$ studied in \cite{KM} and \cite{Kl} give rise to a Hamiltonian
action of the Malcev Lie algebra $\p_n$ of the pure braid group
$P_n$ on the moduli space $M_r$ of $n$gon linkages with the sidelengths
$r= (r_1,\dots, r_n)$ in $\E^3$. If $e\in M_r$ is a singular point we may
linearize the vector fields in $\p_n$ at $e$. This linearization yields a
flat connection $\nabla$ on the space $\C^n_*$ of $n$ distinct points on
$\C$. We show that the monodromy of $\nabla$ is the dual of a quotient
of a specialized reduced Gassner representation.
Categories:53D30, 53D50 
74. CMB 2000 (vol 43 pp. 440)
On the Existence of a New Class of Contact Metric Manifolds A new class of 3dimensional contact metric manifolds is found.
Moreover it is proved that there are no such manifolds in
dimensions greater than 3.
Keywords:contact metric manifolds, generalized $(\kappa,\mu)$contact metric manifolds Categories:53C25, 53C15 
75. CMB 2000 (vol 43 pp. 427)
Helices, Hasimoto Surfaces and BÃ¤cklund Transformations Travelling wave solutions to the vortex filament flow generated by
elastica produce surfaces in $\R^3$ that carry mutually orthogonal
foliations by geodesics and by helices. These surfaces are classified
in the special cases where the helices are all congruent or are all
generated by a single screw motion. The first case yields a new
characterization for the B\"acklund transformation for constant
torsion curves in $\R^3$, previously derived from the wellknown
transformation for pseudospherical surfaces. A similar investigation
for surfaces in $H^3$ or $S^3$ leads to a new transformation for
constant torsion curves in those spaces that is also derived from
pseudospherical surfaces.
Keywords:surfaces, filament flow, BÃ¤cklund transformations Categories:53A05, 58F37, 52C42, 58A15 