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Segre proved that a smooth cubic surface over Q is unirational iff it has a rational point. We prove that the result also holds for cubic hypersurfaces over any field, including finite fields.

Algebraic Geometry · Mathematics 2007-05-23 János Kollár

Let $k$ be an algebraically closed field of characteristic $p>0$, and let $X\subseteq\mathbb{P}^n_k$ be a quasi-projective variety that is $F$-rational and $F$-pure. We prove that if $H \subseteq \mathbb{P}^n_k$ is a general hyperplane,…

Algebraic Geometry · Mathematics 2025-09-30 Alessandro De Stefani , Thomas Polstra , Austyn Simpson

A special linear Lie group over the real number field and the quarternion field admits a projectivley flat affine connection. We show that parabolic subgroups are autoparallel submanifolds and give a criterion the induced connection is…

Differential Geometry · Mathematics 2014-08-19 Hironao Kato

We classify birational maps into elliptic fibrations of a general quasismooth hypersurface in $\mathbb{P}(1,a_{1},a_{2},a_{3},a_{4})$ of degree $\sum_{i=1}^{4}a_{i}$ that has terminal singularities.

Algebraic Geometry · Mathematics 2007-05-23 Ivan Cheltsov

We prove that a smooth, subcanonical surface of P^4 (projective space over an algebraically closed field of characteristic zero) is complete intersection if it is contained in a quartic hypersurface.

Algebraic Geometry · Mathematics 2007-05-23 Ph. Ellia , D. Franco , L. Gruson

In this paper we address Fano foliations on complex projective varieties. These are foliations whose anti-canonical class is ample. We focus our attention on a special class of Fano foliations, namely del Pezzo foliations on complex…

Algebraic Geometry · Mathematics 2012-01-27 Carolina Araujo , Stéphane Druel

We prove that for any rationally connected threefold $X$, there exists a smooth projective surface $S$ and a family of $1$-cycles on $X$ parameterized by $S$, inducing an Abel-Jacobi isomorphism ${\rm Alb}(S)\cong J^3(X)$. This statement…

Algebraic Geometry · Mathematics 2023-04-14 Claire Voisin

A general hypersurface $X$ of degree $\leq n$ in projective space contains curves $C$ of any genus $g\geq 0$ and sufficiently large degree depnding on $g$ whose normal and conormal bundles have good postulation or natural cohomology in the…

Algebraic Geometry · Mathematics 2023-08-07 Ziv Ran

We study unirationality and rationality of Fano threefolds of degree 18 over nonclosed fields.

Algebraic Geometry · Mathematics 2019-10-31 Brendan Hassett , Yuri Tschinkel

The object of the present is a proof of the existence of functorial resolution of tame quotient singularities for quasi-projective varieties over algebraically closed fields.

Algebraic Geometry · Mathematics 2015-11-03 Federico Buonerba

In this text we prove that if a smooth cubic in $\PR^5$ has its Fano variety of lines birational to the Hilbert scheme of two points on a K3 surface, then there exists a smooth projective curve or a smooth projective surface embedded in the…

Algebraic Geometry · Mathematics 2018-04-19 Kalyan Banerjee

We prove that a one-parameter family of rationally connected varieties (over an algebraically closed field of characteristic 0) always has a section.

Algebraic Geometry · Mathematics 2007-05-23 Tom Graber , Joe Harris , Jason Starr

In this paper we try to further explore the linear model of the moduli of rational maps. Our attempt yields following results. Let $X\subset \mathbf P^n$ be a generic hypersurface of degree $h$. Let $R_d(X, h)$ denote the open set of the…

Algebraic Geometry · Mathematics 2015-01-27 Bin Wang

We consider fibrations by affine lines on smooth affine surfaces obtained as complements of smooth rational curves $B$ in smooth projective surfaces $X$ defined over an algebraically closed field of characteristic zero. We observe that…

Algebraic Geometry · Mathematics 2022-05-31 Adrien Dubouloz

In this paper, we study the structure of Fano fibrations of varieties admitting an int-amplified endomorphism. We prove that if a normal $\mathbb{Q}$-factorial klt projective variety $X$ has an int-amplified endomorphism, then there exists…

Algebraic Geometry · Mathematics 2020-02-05 Shou Yoshikawa

We prove the boundedness of $n$-complements for surface pairs in a generalized case without restrictions on multiplicities or the Fano type assumption.

Algebraic Geometry · Mathematics 2023-05-31 Xiangze Zeng

We address the problem of classification of contact Fano manifolds. It is conjectured that every such manifold is necessarily homogeneous. We prove that the Killing form, the Lie algebra grading and parts of the Lie bracket can be read from…

Algebraic Geometry · Mathematics 2021-02-16 Jarosław Buczyński

Metamaterials and meta-surfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, nonlinear optics, and even spaser lasing. Many of these applications rely on the resonant nature of…

We present a manifestly geometrically self-dual version of the Fano harmonicity axiom for the projective plane.

Combinatorics · Mathematics 2017-05-02 P. L. Robinson

A classical result of Bondal-Orlov states that a standard flip in birational geometry gives rise to a fully faithful functor between derived categories of coherent sheaves. We complete their embedding into a semiorthogonal decomposition by…

Algebraic Geometry · Mathematics 2023-02-22 Pieter Belmans , Lie Fu , Theo Raedschelders