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In continuation of our paper in Math. Ann. 333 we classify smooth complex projective threefolds X with -K_X big and nef but not ample and Picard number 2, whose anticanonical map is small. We assume also that the Mori contraction of X and…

Algebraic Geometry · Mathematics 2007-10-16 Priska Jahnke , Thomas Peternell , Ivo Radloff

We use the Clemens-Griffiths method to construct smooth projective threefolds, over any field $k$ admitting a separable quadratic extension, that are $k$-unirational and $\bar{k}$-rational but not $k$-rational. When $k=\mathbb{R}$, we can…

Algebraic Geometry · Mathematics 2020-11-19 Olivier Benoist , Olivier Wittenberg

For any $n\geq 3$, we explicitly construct smooth projective toric $n$-folds of Picard number $\geq 5$, where any nontrivial nef line bundles are big.

Algebraic Geometry · Mathematics 2008-10-24 Osamu Fujino , Hiroshi Sato

We construct singular quartic double fivefolds whose Kuznetsov component admits a crepant categorical resolution of singularities by a twisted Calabi--Yau threefold. We also construct rational specializations of these fivefolds where such a…

Algebraic Geometry · Mathematics 2026-03-10 Raymond Cheng , Alexander Perry , Xiaolei Zhao

We classify projective manifolds with flat holomorphic conformal structures.

Algebraic Geometry · Mathematics 2015-03-02 Priska Jahnke , Ivo Radloff

The authors give a complete classification of projective threefolds admitting a holomorphic conformal structure. A Corollary is the complete list of projective threefolds, whose tangent bundle is a symmetric square.

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

We study linearizability of actions of finite groups on cubic threefolds with nonnodal isolated singularities.

Algebraic Geometry · Mathematics 2025-11-14 Ivan Cheltsov , Lisa Marquand , Yuri Tschinkel , Zhijia Zhang

We classify all 1-nodal degenerations of smooth Fano threefolds with Picard number 1 (both nonfactorial and factorial) and describe their geometry. In particular, we describe a relation between such degenerations and smooth Fano threefolds…

Algebraic Geometry · Mathematics 2024-11-14 Alexander Kuznetsov , Yuri Prokhorov

We investigate when the tangent bundle of a projective manifold has a non-trivial first order (or positive-dimensional) deformation. This leads to a new conjectural characterization of the complex projective space.

Algebraic Geometry · Mathematics 2020-07-20 Thomas Peternell

Let $X$ be a smooth complex projective rationally connected threefold with $-K_X$ nef and not semi-ample. In our previous work, we classified all such threefolds when $|{-}K_X|$ has no fixed divisor. In this paper, we continue our…

Algebraic Geometry · Mathematics 2023-01-24 Zhixin Xie

We study codimension one holomorphic foliations on complex projective spaces and compact manifolds under the assumption that the foliation has a projective transverse structure in the complement of some invariant codimension one analytic…

Dynamical Systems · Mathematics 2010-10-08 Bruno Scardua

In this paper we generalize standard results about non-commutative resolutions of quotient singularities for finite groups to arbitrary reductive groups. We show in particular that quotient singularities for reductive groups always have…

Algebraic Geometry · Mathematics 2017-02-16 Špela Špenko , Michel Van den Bergh

We prove that a nodal quartic threefold $X$ containing no planes is $Q$-factorial provided that it has not more than 12 singular points, with the exception of a quartic with exactly 12 singularities containing a quadric surface. We give…

Algebraic Geometry · Mathematics 2008-03-31 Constantin Shramov

We show that in every dimension greater than or equal to 4, there exist compact Kaehler manifolds which do not have the homotopy type of projective complex manifolds. Thus they a fortiori are not deformation equivalent to a projective…

Algebraic Geometry · Mathematics 2015-08-14 Claire Voisin

We construct a class of noncommutative crepant resolutions of any Kleinian singularity in the form of noncommutative algebras over its crepant partial resolutions. We argue that such resolutions are Morita equivalent to the canonical…

Algebraic Geometry · Mathematics 2025-09-29 Lukas Bertsch

For fixed large genus, we construct families of complete immersed minimal surfaces in R3 with four ends and dihedral symmetries. The families exist for all large genus and at an appropriate scale degenerate to the plane.

Differential Geometry · Mathematics 2014-10-01 Stephen J. Kleene , Niels Martin Moller

We show that certain non-special but weakly special threefolds $X$ constructed by Bogomolov-Tschinkel enjoy strong complex hyperbolicity properties: their entire curves are algebraically degenerate and lie either on a fixed divisor or on…

Algebraic Geometry · Mathematics 2007-05-23 Frederic Campana , Mihai Paun

We study non-variational degenerate elliptic equations with high order singular structures. No boundary data are imposed and singularities occur along an {\it a priori} unknown interior region. We prove that positive solutions have a…

Analysis of PDEs · Mathematics 2016-05-16 Eduardo V. Teixeira

We classify combinations of isolated singularities that can occur on complex cubic threefolds generalizing analogous results for cubic surfaces due to Schl\"{a}fli and Bruce--Wall. In addition, we provide concise combinatorial description…

Algebraic Geometry · Mathematics 2024-05-07 Sasha Viktorova

We show that the connected sum of two copies of real projective 3-space does not admit a real projective structure. This is the first known example of a connected 3-manifold without a real projective structure.

Geometric Topology · Mathematics 2015-01-06 Daryl Cooper , William Goldman