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Let X be a compact Kaehler threefold with terminal singularities such that K\_X is nef. We prove that K\_X is semiample.

Algebraic Geometry · Mathematics 2015-04-21 Frédéric Campana , Andreas Hoering , Thomas Peternell

We prove that a holomorphic line bundle on a projective manifold is pseudo-effective if and only if its degree on any member of a covering family of curves is non-negative. This is a consequence of a duality statement between the cone of…

Algebraic Geometry · Mathematics 2007-05-23 Sébastien Boucksom , Jean-Pierre Demailly , Mihai Paun , Thomas Peternell

The authors give a complete classification of projective threefolds admitting a holomorphic normal projective connection. Moreover, they prove a general structure theorem on complex projective manifolds admitting a holomorphic normal…

Algebraic Geometry · Mathematics 2007-05-23 Priska Jahnke , Ivo Radloff

We classify all smooth compact connected K\"ahler threefolds that admit the structure of a $C^\infty$-fiber bundle over the circle. This generalizes the work of Hao and Schreieder in the projective case. In contrast to the projective case,…

Algebraic Geometry · Mathematics 2025-06-30 Simon Pietig

In this paper, we prove that a compact K\"ahler manifold $X$ with the nef anti-canonical bundle $-K_{X}$ admits a locally trivial fibration $\phi \colon X \to Y$, where the fiber $F$ is a rationally connected manifold and the base $Y$ is a…

Algebraic Geometry · Mathematics 2025-07-01 Shin-ichi Matsumura , Juanyong Wang , Xiaojun Wu , Qimin Zhang

In this article we show that if $(X, \Delta)$ is a log canonical compact K\"ahler threefold pair such that $K_X+\Delta$ is nef and the numerical dimension $\nu(X, K_X+\Delta)=2$, then $K_X+\Delta$ is semi-ample. This result combined with…

Algebraic Geometry · Mathematics 2025-06-13 Omprokash Das , Wenhao Ou

We conjecture that certain curvature invariants of compact hyperk\"ahler manifolds are positive/negative. We prove the conjecture in complex dimension four, give an "experimental proof" in higher dimensions, and verify it for all known…

Differential Geometry · Mathematics 2021-12-23 Justin Sawon

For every compact K\"ahler manifold $X$ of algebraic dimension $a(X) = \dim X - 1$, we prove that $X$ has arbitrarily small deformations to some projective manifolds.

Algebraic Geometry · Mathematics 2020-12-16 Hsueh-Yung Lin

We study the local geometry of the moduli space of intermediate Jacobians of $(2,2)$-threefolds in ${\mathbb P}^2 \times {\mathbb P}^2$. More precisely, we prove that a composition of the second fundamental form of the Siegel metric in…

Algebraic Geometry · Mathematics 2023-10-17 Elisabetta Colombo , Paola Frediani , Juan Carlos Naranjo , Gian Pietro Pirola

In this paper, we study the moduli spaces of canonical threefolds with any prescribed geometric genus $p_g \ge 5$ which have the smallest possible canonical volume. This minimal volume is equal to the smallest half-integer that is larger…

Algebraic Geometry · Mathematics 2025-11-04 Stephen Coughlan , Yong Hu , Roberto Pignatelli , Tong Zhang

Let M be a (bounded or not) domain of C^n which is complete with respect to a K\"ahler metric, or more generally, a complete K\"ahler manifold with trivial canonical bundle. Let f be a linearly nondegenerate meromorphic map from M to the…

Complex Variables · Mathematics 2017-11-13 Do Duc Thai , Duc-Viet Vu

The notion of Kodaira dimension has recently been extended to general almost complex manifolds. In this paper we focus on the Kodaira dimension of almost K\"ahler manifolds, providing an explicit computation for a family of almost K\"ahler…

Differential Geometry · Mathematics 2019-09-04 Andrea Cattaneo , Antonella Nannicini , Adriano Tomassini

1) We give a 3-dimensional analogue of M. Noether's inequality for canonically polarized threefolds: $K^3\ge 2(2p_g-5)/3$. This inequality is sharp by known examples of M. Kobayashi. 2) Given a minimal 3-fold $X$ of general type with…

Algebraic Geometry · Mathematics 2007-05-23 Meng Chen

In this paper, for compact K\"ahler manifolds with nef cotangent bundle, we study the abundance conjecture and the associated Iitaka fibrations. We show that, for a minimal compact K\"ahler manifold, the second Chern class vanishes if and…

Algebraic Geometry · Mathematics 2022-05-24 Masataka Iwai , Shin-ichi Matsumura

In the present paper, we show that given a compact K\"ahler manifold $(X,\omega)$ with a K\"ahler metric $\omega$, and a complex submanifold $V\subset X$ of positive dimension, if $V$ has a holomorphic retraction structure in $X$, then any…

Complex Variables · Mathematics 2021-05-19 Jiafu Ning , Zhiwei Wang , Xiangyu Zhou

We prove that any compact K\"ahler 3-dimensional manifold which has no non-trivial complex subvarieties is a torus. This is a very special case of a general conjecture on the structure of 'simple manifolds', central in the bimeromorphic…

Algebraic Geometry · Mathematics 2014-01-16 Frédéric Campana , Jean-Pierre Demailly , Misha Verbitsky

We prove compactification theorems for some complete K\"ahler manifolds with nonnegative Ricci curvature. Among other things, we prove that a complete noncompact K\"ahler Ricci flat manifold with maximal volume growth and quadratic…

Differential Geometry · Mathematics 2017-06-20 Gang Liu

Following the first paper, we continue to study Mori extractions from singular curves centred in a smooth 3-fold. We treat the case where the divisorial extraction exists in relative codimension at most 3.

Algebraic Geometry · Mathematics 2016-09-09 Tom Ducat

We show that the $\partial\bar{\partial}$-lemma holds for the non-K\"ahler compact complex manifolds of dimension three with trivial canonical bundle constructed by Clemens as deformations of Calabi-Yau threefolds contracted along smooth…

Algebraic Geometry · Mathematics 2020-03-17 Robert Friedman

In the first part of this note, we discuss the compact K\"ahler manifold with a strongly pseudo-effective tangent bundle. In the second part, we give new proof of the fact that the only projective manifolds with the big tangent bundle are…

Differential Geometry · Mathematics 2024-01-02 Xiaojun Wu