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Sobre subvariedades totalmente reais / On totally real submanifoldsJosà Loester Sà Carneiro 05 July 2011 (has links)
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Subvariedades analÃticas complexas e totalmente reais sÃo duas classes tÃpicas dentre todas as subvariedades de uma variedade quase Hermitiana. Neste trabalho procuramos dar algumas caracterizaÃÃes de subvariedades totalmente reais. AlÃm disso algumas classificaÃÃes de subvariedades totalmente reais em formas espaciais complexas sÃo obtidas. / Complex analytic submanifolds and totally real submanifolds are two typical classes among all submanifolds of an almost Hermitian manifolds. In this work, some characterizations of totally real submanifolds are given. Moreover some classifications of totally real submanifolds in complex space forms are obtained.
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The differential geometry of the fibres of an almost contract metric submersionTshikunguila, Tshikuna-Matamba 10 1900 (has links)
Almost contact metric submersions constitute a class of Riemannian submersions whose
total space is an almost contact metric manifold. Regarding the base space, two types
are studied. Submersions of type I are those whose base space is an almost contact
metric manifold while, when the base space is an almost Hermitian manifold, then the
submersion is said to be of type II.
After recalling the known notions and fundamental properties to be used in the
sequel, relationships between the structure of the fibres with that of the total space
are established. When the fibres are almost Hermitian manifolds, which occur in the
case of a type I submersions, we determine the classes of submersions whose fibres
are Kählerian, almost Kählerian, nearly Kählerian, quasi Kählerian, locally conformal
(almost) Kählerian, Gi-manifolds and so on. This can be viewed as a classification of
submersions of type I based upon the structure of the fibres.
Concerning the fibres of a type II submersions, which are almost contact metric
manifolds, we discuss how they inherit the structure of the total space.
Considering the curvature property on the total space, we determine its corresponding
on the fibres in the case of a type I submersions. For instance, the cosymplectic
curvature property on the total space corresponds to the Kähler identity on the fibres.
Similar results are obtained for Sasakian and Kenmotsu curvature properties.
After producing the classes of submersions with minimal, superminimal or umbilical
fibres, their impacts on the total or the base space are established. The minimality of
the fibres facilitates the transference of the structure from the total to the base space.
Similarly, the superminimality of the fibres facilitates the transference of the structure
from the base to the total space. Also, it is shown to be a way to study the integrability
of the horizontal distribution.
Totally contact umbilicity of the fibres leads to the asymptotic directions on the total
space.
Submersions of contact CR-submanifolds of quasi-K-cosymplectic and
quasi-Kenmotsu manifolds are studied. Certain distributions of the under consideration
submersions induce the CR-product on the total space. / Mathematical Sciences / D. Phil. (Mathematics)
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The differential geometry of the fibres of an almost contract metric submersionTshikunguila, Tshikuna-Matamba 10 1900 (has links)
Almost contact metric submersions constitute a class of Riemannian submersions whose
total space is an almost contact metric manifold. Regarding the base space, two types
are studied. Submersions of type I are those whose base space is an almost contact
metric manifold while, when the base space is an almost Hermitian manifold, then the
submersion is said to be of type II.
After recalling the known notions and fundamental properties to be used in the
sequel, relationships between the structure of the fibres with that of the total space
are established. When the fibres are almost Hermitian manifolds, which occur in the
case of a type I submersions, we determine the classes of submersions whose fibres
are Kählerian, almost Kählerian, nearly Kählerian, quasi Kählerian, locally conformal
(almost) Kählerian, Gi-manifolds and so on. This can be viewed as a classification of
submersions of type I based upon the structure of the fibres.
Concerning the fibres of a type II submersions, which are almost contact metric
manifolds, we discuss how they inherit the structure of the total space.
Considering the curvature property on the total space, we determine its corresponding
on the fibres in the case of a type I submersions. For instance, the cosymplectic
curvature property on the total space corresponds to the Kähler identity on the fibres.
Similar results are obtained for Sasakian and Kenmotsu curvature properties.
After producing the classes of submersions with minimal, superminimal or umbilical
fibres, their impacts on the total or the base space are established. The minimality of
the fibres facilitates the transference of the structure from the total to the base space.
Similarly, the superminimality of the fibres facilitates the transference of the structure
from the base to the total space. Also, it is shown to be a way to study the integrability
of the horizontal distribution.
Totally contact umbilicity of the fibres leads to the asymptotic directions on the total
space.
Submersions of contact CR-submanifolds of quasi-K-cosymplectic and
quasi-Kenmotsu manifolds are studied. Certain distributions of the under consideration
submersions induce the CR-product on the total space. / Mathematical Sciences / D. Phil. (Mathematics)
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Géométrie et dynamique des structures Hermite-Lorentz / Geometry and Dynamics of Hermite-Lorentz structuresBen Ahmed, Ali 06 July 2013 (has links)
Dans la veine du programme d'Erlangen de Klein, travaux d'E. Cartan, M. Gromov, et d'autres, ce travail se trouve à cheval, entre la géométrie et les actions de groupes. Le thème global serait de comprendre les groupes d'isométries des variétés pseudo-riemanniennes. Plus précisément, suivant une "conjecture vague" de Gromov, classifier les variétés pseudo-riemanniennes dont le groupe d'isométries agit non-proprement, i.e. que son action ne préserve pas de métrique riemannienne auxiliaire?Plusieurs travaux ont été accomplis dans le cas des métriques lorentziennes (i.e. de signature (- +...+)). En revanche, le cas pseudo-riemannien général semble hors de portée.Les structures Hermite-Lorentz se trouvent entre le cas lorentzien et le premier cas pseudo-riemannien général, i.e. de signature (- - +…+). De plus, elle se définit sur des variétés complexes, et promet une extra-rigidité. Plus précisément, une structure Hermite-Lorentz sur une variété complexe consiste en une métrique pseudo-riemannienne de signature (- - +…+) qui est hermitienne au sens qu'elle est invariante par la structure presque complexe. Par analogie au cas hermitien classique, on définit naturellement une notion de métrique Kähler-Lorentz.Comme exemple, on a l'espace de Minkowski complexe ; dans un certain sens, on a un temps de dimension 1 complexe (du point de vue réel, le temps est 2-dimensionnel). On a également l'espace de Sitter et anti de Sitter complexes. Ils ont une courbure holomorphe constante, et généralisent dans ce sens les espaces projectifs et hyperboliques complexes.Cette thèse porte sur les variétés Hermite-Lorentz homogènes. En plus des exemples cités, il y a deux autres espaces symétriques, qui peuvent naturellement jouer le rôle de complexification des espaces de Sitter et anti de Sitter réels.Le résultat principal de la thèse est un théorème de rigidité de ces espaces symétriques : tout espace Hermite-Lorentz homogène à isotropie irréductible est l'un des cinq espaces symétriques précédents. D'autres résultats concernent le cas où l'on remplace l'hypothèse d'irréductibilité par le fait que le groupe d'isométries soit semi-simple. / In the vein of Klein's Erlangen program, the research works of E. Cartan, M.Gromov and others, this work straddles between geometry and group actions. The overall theme is to understand the isometry groups of pseudo-Riemannian manifolds. Precisely, following a "vague conjecture" of Gromov, our aim is to classify Pseudo-Riemannian manifolds whose isometry group act’s not properly, i.e that it’s action does not preserve any auxiliary Riemannian metric. Several studies have been made in the case of the Lorentzian metrics (i.e of signature (- + .. +)). However, general pseudo-Riemannian case seems out of reach. The Hermite-Lorentz structures are between the Lorentzian case and the former general pseudo-Riemannian, i.e of signature (- -+ ... +). In addition, it’s defined on complex manifolds, and promises an extra-rigidity. More specifically, a Hermite-Lorentz structure on a complex manifold is a pseudo-Riemannian metric of signature (- -+ ... +), which is Hermitian in the sense that it’s invariant under the almost complex structure. By analogy with the classical Hermitian case, we naturally define a notion of Kähler-Lorentz metric. We cite as example the complex Minkowski space in where, in a sense, we have a one-dimensional complex time (the real point of view, the time is two-dimensional). We cite also the de Sitter and Anti de Sitter complex spaces. They have a constant holomorphic curvature, and generalize in this direction the projective and complex hyperbolic spaces.This thesis focuses on the Hermite-Lorentz homogeneous spaces. In addition with given examples, two other symmetric spaces can naturally play the role of complexification of the de Sitter and anti de Sitter real spaces.The main result of the thesis is a rigidity theorem of these symmetric spaces: any space Hermite-Lorentz isotropy irreducible homogeneous is one of the five previous symmetric spaces. Other results concern the case where we replace the irreducible hypothesis by the fact that the isometry group is semisimple.
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