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Let $(X, A)$ be a nonsingular polarized toric 3-fold. We show that if the adjoint bundle of $A$ has no glabal section, then all ample line bundles on $X$ are normally generated. Even if the adjoint bundle is effective, if it is not big,…

Algebraic Geometry · Mathematics 2014-04-29 Shoetsu Ogata

We obtain a sufficient condition for a Fano threefold with terminal singularities to have a conic bundle structure.

Algebraic Geometry · Mathematics 2022-02-02 Yuri Prokhorov

We prove that any Fano manifold of coindex three admitting nef tangent bundle is homogeneous.

Algebraic Geometry · Mathematics 2019-04-24 Kiwamu Watanabe

Projective spaces for finite-dimensional vector spaces over general fields are considered. The geometry of these spaces and the theory of line bundles over these spaces is presented. Particularly, the space of global regular sections of…

Algebraic Geometry · Mathematics 2023-09-21 Andrew D. Lewis

We study smooth projective complex varieties with ample cotangent bundle. Our main result is that in an abelian variety of dimension n, a complete intersection of at least n/2 general hypersurfaces of sufficiently high degrees has ample…

Algebraic Geometry · Mathematics 2011-09-08 O. Debarre

In this work we prove on a given smooth toric threefold all but finitely many ample line bundles are projectively normal.

Algebraic Geometry · Mathematics 2023-09-12 He Xin

Using Hultgren's polytope formulation of the existence of coupled K\"ahler-Einstein (cKE) metrics on toric Fano manifolds, we construct explicit higher-dimensional toric Fano manifolds that admit two coupled K\"ahler-Einstein metrics but no…

Differential Geometry · Mathematics 2026-02-25 Naoto Yotsutani

On a projective surface it is well-known that the set of curves orthogonal to a nef line bundle is either finite or uncountable. We show that this dichotomy fails in higher dimension by constructing a nef line bundle on a threefold which is…

Algebraic Geometry · Mathematics 2014-10-17 John Lesieutre , John Christian Ottem

Any smooth projective variety contains many complete intersection subvarieties with ample cotangent bundles, of each dimension up to half its own dimension.

Algebraic Geometry · Mathematics 2017-12-11 Damian Brotbek , Lionel Darondeau

The aim of this note is to exhibit explicit sufficient criteria ensuring bigness of globally generated, rank-$r$ vector bundles, $r \geqslant 2$, on smooth, projective varieties of even dimension $d \leqslant 4$. We also discuss connections…

Algebraic Geometry · Mathematics 2019-11-05 Gilberto Bini , Flaminio Flamini

We propose a notion of instanton bundle (called $H$-instanton bundle) on any projective variety of dimension three polarized by a very ample divisor $H$, that naturally generalizes the ones on $\mathbb{P}^3$ and on the flag threefold…

Algebraic Geometry · Mathematics 2020-11-26 Vincenzo Antonelli , Francesco Malaspina

For a Fano threefold admitting a full exceptional collection of vector bundles of length four we show that all full exceptional collections consist of shifted vector bundles. We prove this via a detailed study of the group generated by…

Algebraic Geometry · Mathematics 2026-02-16 Anya Nordskova , Michel Van den Bergh

We prove that a projective contact manifold X with second Betti number at least 2 whose canonical bundle K_X is not nef, is always the projectivised tangent bundle P(T_Y) of a projective manifold Y. It is expected that the canonical bundle…

Algebraic Geometry · Mathematics 2007-05-23 Stefan Kebekus , Thomas Peternell , Andrew J. Sommese , Jaroslaw Wisniewski

In this article, we investigate Serrano's conjecture for strictly nef divisors on projective bundles over higher dimensional smooth projective varieties.

Algebraic Geometry · Mathematics 2024-05-10 Snehajit Misra

We study codimension one holomorphic distributions on the projective three-space, analyzing the properties of their singular schemes and tangent sheaves. In particular, we provide a classification of codimension one distributions of degree…

Algebraic Geometry · Mathematics 2021-08-03 Omegar Calvo-Andrade , Maurício Corrêa , Marcos Jardim

Chow's Theorem and GAGA are renowned results demonstrating the algebraic nature of projective manifolds and, more broadly, projective analytic varieties. However, determining if a particular manifold is projective is not, generally, a…

Algebraic Geometry · Mathematics 2025-01-14 Skyler Marks

We investigate the structure of smooth holomorphic foliations with numerically flat tangent bundles on compact K\"ahler manifolds. Extending earlier results on non-uniruled projective manifolds by the second and fourth authors, we show that…

Algebraic Geometry · Mathematics 2024-11-14 Stéphane Druel , Jorge Vitório Pereira , Brent Pym , Frédéric Touzet

The cellular resolution of the diagonal given by Bayer-Popescu-Sturmfels for unimodular projective toric varieties yields a full, strong exceptional collection of line bundles on unimodular projective toric surfaces. The…

Algebraic Geometry · Mathematics 2024-05-17 Reginald Anderson

We show that a nef and big line bundle whose adjoint bundle has non-zero global sections on a nonsingular toric weak Fano 3-fold is normally generated. As a consequence, we see that all ample line bundles on a nonsingular toric weak Fano…

Algebraic Geometry · Mathematics 2013-10-25 Shoetsu Ogata

We classify compact K\"ahler manifolds with semi-positive holomorphic bisectional and big tangent bundles. We also classify compact complex surfaces with semi-positive tangent bundles and compact complex $3$-folds of the form $P(T^*X)$…

Differential Geometry · Mathematics 2015-04-24 Xiaokui Yang