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In this article, we first describe codimension two regular foliations with numerically trivial canonical class on complex projective manifolds whose canonical class is not numerically effective. Building on a recent algebraicity criterion…

Algebraic Geometry · Mathematics 2023-06-22 Stéphane Druel

Contents 1. Algebraicity criterion: statement 2. Proof of the algebraicity criterion. 3. Pseudoeffectivity and movable classes. 4. Harder-Narasimhan filtrations and pseudo-effectivity. 5. Pseudo-effectivity of relative canonical bundles. 6.…

Algebraic Geometry · Mathematics 2021-12-24 Frederic Campana

The classical Beauville-Bogomolov Decomposition Theorem asserts that any compact K\"ahler manifold with numerically trivial canonical bundle admits an \'etale cover that decomposes into a product of a torus, and irreducible,…

Algebraic Geometry · Mathematics 2016-11-08 Daniel Greb , Stefan Kebekus , Thomas Peternell

We give a simplified proof (in characteristic zero) of the decomposition theorem for complex projective varieties with klt singularities and numerically trivial canonical bundle. The proof rests in an essential way on most of the partial…

Algebraic Geometry · Mathematics 2020-05-13 Frederic Campana

In this article we consider log canonical pairs which are log-smooth. If the corresponding canonical bundle is pseudo-effective, then we show that any quotient of the orbifold cotangent bundle of the pair has a pseudo-effective determinant.…

Algebraic Geometry · Mathematics 2017-06-16 Frederic Campana , Mihai Paun

Let $X$ be a compact complex manifold such that its canonical bundle $K_X$ is numerically trivial. Assume additionally that $X$ is Moishezon or $X$ is Fujiki with dimension at most four. Using the MMP and classical results in foliation…

Differential Geometry · Mathematics 2024-09-11 Indranil Biswas , Junyan Cao , Sorin Dumitrescu , Henri Guenancia

In this paper we partly extend the Beauville-Bogomolov decomposition theorem to the singular setting. We show that any complex projective variety of dimension at most five with canonical singularities and numerically trivial canonical class…

Algebraic Geometry · Mathematics 2016-06-30 Stéphane Druel

We show that an everywhere regular foliation $\mathcal F$ with compact canonically polarized leaves on a quasi-projective manifold $X$ has isotrivial family of leaves when the orbifold base of this family is special. By a recent work of…

Algebraic Geometry · Mathematics 2017-09-22 Ekaterina Amerik , Frédéric Campana

We discuss residue formulae that localize the first Chern class of a line bundle to the singular locus of a given holomorphic connection. As an application, we explain a proof for Brunella's conjecture about exceptional minimal sets of…

Complex Variables · Mathematics 2023-08-17 Masanori Adachi , Séverine Biard , Judith Brinkschulte

We investigate the holonomy group of singular K\"ahler-Einstein metrics on klt varieties with numerically trivial canonical divisor. Finiteness of the number of connected components, a Bochner principle for holomorphic tensors, and a…

Algebraic Geometry · Mathematics 2020-06-16 Daniel Greb , Henri Guenancia , Stefan Kebekus

We identify a class of singular algebraic foliations whose leaves through singular points retain regularity. The proof consists in showing existence of residual gerbes for certain formal stacks, which do not enjoy smooth presentations. As…

Algebraic Geometry · Mathematics 2025-10-24 Federico Bongiorno

This paper is concerned with a sufficient criterion to guarantee that a given foliation on a normal variety has algebraic and rationally connected leaves. Following ideas from a preprint of Bogomolov-McQuillan and using recent works of…

Algebraic Geometry · Mathematics 2009-09-29 Stefan Kebekus , Luis Sola Conde , Matei Toma

Let ${\mathbb F}_0$ be an algebraically closed field, with $char({\mathbb F}_0)=0$. In this article, for prime numbers $p\geq 2$, we construct smooth affine algebras $B$ over ${\mathbb F}_0$, with $\dim B=p+2$. Further, we construct…

K-Theory and Homology · Mathematics 2026-03-10 Satya Mandal

Four-folds with trivial canonical bundles are divided into six classes according to their holonomy group. We consider examples that are fibred by abelian surfaces over the projective plane. We construct such fibrations in five of the six…

Algebraic Geometry · Mathematics 2015-12-01 Justin Sawon

For any admissible subcategory of the bounded derived category of coherent sheaves on a smooth proper variety, we prove that sections of the canonical bundle impose a strong constraint on the supports of the objects of the subcategory or…

Algebraic Geometry · Mathematics 2018-09-05 Kotaro Kawatani , Shinnosuke Okawa

We prove the existence (in characteristic 0) on every polarized (smooth, projective and connected) surface of stable bundles of rank $r\geq 2$, arbitrary first Chern class and large enough $c_2$.

alg-geom · Mathematics 2008-02-03 André Hirschowitz , Yves Laszlo

We give a criterion for the projectivisation of a reflexive sheaf on a klt space to be induced by a projective representation of the fundamental group of the smooth locus. This criterion is then applied to give a characterisation of finite…

Algebraic Geometry · Mathematics 2022-07-25 Daniel Greb , Stefan Kebekus , Thomas Peternell

We give a criterion for a flat fibration with affine plane fibers over a smooth scheme defined over a field of characteristic zero to be a Zariski locally trivial $\mathbb{A}^2$-bundle. An application is a positive answer to a version of…

Algebraic Geometry · Mathematics 2017-04-17 Adrien Dubouloz

Assume that $X$ is a compact complex analytic variety which has quotient singularities in codimension 2, and that $\mathcal{F}$ is a reflexive sheaf on $X$. Using orbifold modifications, we can define first and second homological Chern…

Algebraic Geometry · Mathematics 2025-12-30 Wenhao Ou

This paper extends a number of known results on slope-semistable sheaves from the classical case to the setting where polarisations are given by movable curve classes. As applications, we obtain new flatness results for reflexive sheaves on…

Algebraic Geometry · Mathematics 2016-06-28 Daniel Greb , Stefan Kebekus , Thomas Peternell
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