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We consider the following conjecture: if X is a smooth projective variety over a field of characteristic zero, then there is a dense set of reductions X_s of X to positive characteristic such that the action of the Frobenius morphism on the…

Commutative Algebra · Mathematics 2011-06-02 Mircea Mustata , Vasudevan Srinivas

Given a complex projective manifold $X$ and a divisor $D$ with normal crossings, we say that the logarithmic tangent bundle $T_X(-\log D)$ is R-flat if its pull-back to the normalization of any rational curve contained in $X$ is the trivial…

Algebraic Geometry · Mathematics 2020-08-07 Stéphane Druel , Federico Lo Bianco

A natural explicit condition is given ensuring that an action of the multiplicative monoid of non-negative reals on a manifold F comes from homotheties of a vector bundle structure on F, or, equivalently, from an Euler vector field. This is…

Differential Geometry · Mathematics 2010-05-28 Janusz Grabowski , Mikolaj Rotkiewicz

One version of the classical Lefschetz hyperplane theorem states that for $U \subset \mathbb P^n$ a smooth quasi-projective variety of dimension at least $2$, and $H \cap U$ a general hyperplane section, the resulting map on \'etale…

Algebraic Geometry · Mathematics 2020-05-22 Aaron Landesman

In response to a question of Reid, we find all anti-canonical Calabi-Yau hypersurfaces $X$ in toric weighted projective bundles over the projective line where the general fiber is a weighted K3 hypersurface. This gives a direct…

Algebraic Geometry · Mathematics 2007-05-23 Joshua P. Mullet

For smooth families with maximal variation, whose general fibers have semi-ample canonical bundle, the generalized Viehweg hyperbolicity conjecture states that the base spaces of such families are of log general type. This deep conjecture…

Algebraic Geometry · Mathematics 2020-05-01 Ya Deng , with an appendix by Dan Abramovich

In an earlier paper we conjectured a relation between the quantum $\mathcal D$-modules of a smooth variety $X$ and the projectivisation of a direct sum of line bundles over it. In this paper we prove the conjecture when $X$ is a complete…

Algebraic Geometry · Mathematics 2007-05-23 Artur Elezi

We study the algebraic hyperbolicity of certain subvarieties of homogeneous varieties, building on the techniques introduced by Coskun-Riedl, Yeong and Mioranci. This generalizes earlier known results for hypersurfaces to higher…

Algebraic Geometry · Mathematics 2025-11-10 Andy B. Day , Neelarnab Raha

The classical Shafarevich conjecture predicts that the universal cover of a complex smooth projective variety $X$ is holomorphically convex. In this paper, we propose a refinement of this conjecture for varieties defined over the reals. In…

Algebraic Geometry · Mathematics 2026-03-19 Rodolfo Aguilar , Cristhian Garay

The geometric torsion conjecture asserts that the torsion part of the Mordell--Weil group of a family of abelian varieties over a complex quasiprojective curve is uniformly bounded in terms of the genus of the curve. We prove the conjecture…

Algebraic Geometry · Mathematics 2015-04-09 Benjamin Bakker , Jacob Tsimerman

The aim of these notes is to acquaint the reader with important objects in complex algebraic geometry: K3 surfaces and their higher-dimensional analogs, hyperk\"ahler manifolds. These manifolds are interesting from several points of view:…

Algebraic Geometry · Mathematics 2020-11-18 Olivier Debarre

Let X be a smooth projective curve of genus >1 over a field K which is finitely generated over the rationals. The section conjecture in Grothendieck's anabelian geometry says that the sections of the canonical projection from the arithmetic…

Algebraic Geometry · Mathematics 2007-05-23 Jochen Koenigsmann

Let $X$ be a smooth irreducible complex algebraic variety of dimension $n$ and $L$ a very ample line bundle on $X$. Given a toric degeneration of $(X,L)$ satisfying some natural technical hypotheses, we construct a deformation $\{J_s\}$ of…

Symplectic Geometry · Mathematics 2018-03-02 Mark Hamilton , Megumi Harada , Kiumars Kaveh

We investigate relation between Dehn fillings and commensurability of hyperbolic 3-manifolds. The set consisting of the commensurability classes of hyperbolic 3-manifolds admits the quotient topology induced by the geometric topology. We…

Geometric Topology · Mathematics 2022-03-17 Ken'ichi Yoshida

We give a simple combinatorial proof of the toric version of Mori's theorem that the only $n$-dimensional smooth projective varieties with ample tangent bundle are the projective spaces $\mathbb{P}^n$.

Algebraic Geometry · Mathematics 2022-10-05 Kuang-Yu Wu

Let B be a nef and big line bundle on a smooth complex threefold X with canonical bundle K. Let x be a point on X and suppose that BC\ge3 for any curve C passing x, B^2S\ge7 for any surface S containing x, and B^3\ge51. Then K+B is spanned…

alg-geom · Mathematics 2008-02-03 Takao Fujita

Hypertoric varieties are hyperk\"ahler analogues of toric varieties, and are constructed as abelian hyperk\"ahler quotients of a quaternionic affine space. Just as symplectic toric orbifolds are determined by labelled polytopes, orbifold…

Differential Geometry · Mathematics 2009-09-10 Rebecca Goldin , Megumi Harada

In 1970, Kobayashi conjectured that general hypersurfaces of sufficiently large degree in $P^n$ are hyperbolic. In this paper we prove that a general sufficiently ample hypersurface in a smooth projective variety is hyperbolic. To prove…

Algebraic Geometry · Mathematics 2016-07-04 Damian Brotbek

We confirm Beauville's conjecture that claims that if the p-th exterior power of the tangent bundle of a smooth projective variety contains the p-th power of an ample line bundle, then the variety is either the projective space or the…

Algebraic Geometry · Mathematics 2009-11-13 Carolina Araujo , Stéphane Druel , Sándor J. Kovács

We complete the proof of the Nisnevich conjecture in equal characteristic: for a smooth algebraic variety $X$ over a field $k$, a $k$-smooth divisor $D \subset X$, and a reductive $X$-group $G$ whose base change $G_D$ is totally isotropic,…

Algebraic Geometry · Mathematics 2025-12-09 Kestutis Cesnavicius