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Sur les orbites d’un sous-groupe sphérique dans la variété des drapeaux

Nicolas Ressayre (2004)

Bulletin de la Société Mathématique de France

Soient G un groupe algébrique complexe réductif et connexe, B un sous-groupe de Borel de G et H un sous-groupe sphérique de G . Soit X un plongement G × G -équivariant de G . Nous savons que B × H n’a qu’un nombre fini d’orbites dans G  ; nous montrons qu’il n’en a qu’un nombre fini dans X . Soit V ¯ l’adhérence dans X d’une orbite de B × H dans G et 𝒪 ¯ l’adhérence d’une orbite de G × G dans X . Si X est toroïdal, nous montrons que l’intersection V ¯ 𝒪 ¯ est propre dans X et la décrivons ensemblistement. Si de plus X est lisse,...

The abelianization of the Johnson kernel

Alexandru Dimca, Richard Hain, Stefan Papadima (2014)

Journal of the European Mathematical Society

We prove that the first complex homology of the Johnson subgroup of the Torelli group T g is a non-trivial, unipotent T g -module for all g 4 and give an explicit presentation of it as a S y m . H 1 ( T g , C ) -module when g 6 . We do this by proving that, for a finitely generated group G satisfying an assumption close to formality, the triviality of the restricted characteristic variety implies that the first homology of its Johnson kernel is a nilpotent module over the corresponding Laurent polynomial ring, isomorphic to the...

The BIC of a singular foliation defined by an abelian group of isometries

Martintxo Saralegi-Aranguren, Robert Wolak (2006)

Annales Polonici Mathematici

We study the cohomology properties of the singular foliation ℱ determined by an action Φ: G × M → M where the abelian Lie group G preserves a riemannian metric on the compact manifold M. More precisely, we prove that the basic intersection cohomology * p ̅ ( M / ) is finite-dimensional and satisfies the Poincaré duality. This duality includes two well known situations: ∙ Poincaré duality for basic cohomology (the action Φ is almost free). ∙ Poincaré duality for intersection cohomology (the group G is compact...

The cobordism of Real manifolds

Po Hu (1999)

Fundamenta Mathematicae

We calculate completely the Real cobordism groups, introduced by Landweber and Fujii, in terms of homotopy groups of known spectra.

The cohomology algebra of certain free loop spaces

Toshihiro Yamaguchi, Katsuhiko Kuribayashi (1997)

Fundamenta Mathematicae

Let X be a simply connected space and LX the space of free loops on X. We determine the mod p cohomology algebra of LX when the mod p cohomology of X is generated by one element or is an exterior algebra on two generators. We also provide lower bounds on the dimensions of the Hodge decomposition factors of the rational cohomology of LX when the rational cohomology of X is a graded complete intersection algebra. The key to both of these results is the identification of an important subalgebra of...

The cohomology algebras of orientable Seifert manifolds and applications to Lusternik-Schnirelmann category

J. Bryden, P. Zvengrowski (1998)

Banach Center Publications

This note gives a complete description of the cohomology algebra of any orientable Seifert manifold with ℤ/p coefficients, for an arbitrary prime p. As an application, the existence of a degree one map from an orientable Seifert manifold onto a lens space is completely determined. A second application shows that the Lusternik-Schnirelmann category for a large class of Seifert manifolds is equal to 3, which in turn is used to verify the Ganea conjecture for these Seifert manifolds.

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