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Projectivity of Kähler manifolds – Kodaira’s problem

Daniel Huybrechts (2005/2006)

Séminaire Bourbaki

Every compact Kähler surface is deformation equivalent to a projective surface. In particular, topologically Kähler surfaces and projective surfaces cannot be distinguished. Kodaira had asked whether this continues to hold in higher dimensions. We explain the construction of a series of counter-examples due to C. Voisin, which yields compact Kähler manifolds of dimension at least four whose rational homotopy type is not realized by any projective manifold.

Prolongements en fonctions algébriquement constructibles.

Isabelle Bonnard-Doré (2004)

Revista Matemática Complutense

In this paper we consider the following question: Let S be a semialgebraic subset of a real algebraic set V, and let φ: S → Z be a function on S. Is φ the restriction of an algebraically constructible function on V, i.e. a sum of signs of polynomials on V? We give an effective method to answer this question when φ(S) ⊂ {-1,1} or dim S ≤ 2 or S is basic.

Proof of Nadel’s conjecture and direct image for relative K -theory

Alain Berthomieu (2002)

Bulletin de la Société Mathématique de France

A “relative” K -theory group for holomorphic or algebraic vector bundles on a compact or quasiprojective complex manifold is constructed, and Chern-Simons type characteristic classes are defined on this group in the spirit of Nadel. In the projective case, their coincidence with the Abel-Jacobi image of the Chern classes of the bundles is proved. Some applications to families of holomorphic bundles are given and two Riemann-Roch type theorems are proved for these classes.

Proof of the Knop conjecture

Ivan V. Losev (2009)

Annales de l’institut Fourier

In this paper we prove the Knop conjecture asserting that two smooth affine spherical varieties with the same weight monoid are equivariantly isomorphic. We also state and prove a uniqueness property for (not necessarily smooth) affine spherical varieties.

Properties of subgroups not containing their centralizers

Lemnouar Noui (2009)

Annales mathématiques Blaise Pascal

In this paper, we give a generalization of Baer Theorem on the injective property of divisible abelian groups. As consequences of the obtained result we find a sufficient condition for a group G to express as semi-direct product of a divisible subgroup D and some subgroup H . We also apply the main Theorem to the p -groups with center of index p 2 , for some prime p . For these groups we compute N c ( G ) the number of conjugacy classes and N a the number of abelian maximal subgroups and N n a the number of nonabelian...

Propriétés de descente des variétés à fibré cotangent ample

Mireille Martin-Deschamps (1984)

Annales de l'institut Fourier

On généralise ici un théorème de Grauert-Manin pour les courbes (problème de Mordell pour les corps de fonctions). Soit L un corps de fonctions algébriques sur un corps algébriquement clos k de caractéristique 0, X une variété propre et lisse sur L , dont le fibré cotangent Ω X / L 1 est ample; si l’ensemble de ses points rationnels est Zariski-dense, la variété X se redescend sur k .

Currently displaying 341 – 360 of 397