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In this article we consider exceptional sequences of invertible sheaves on smooth complete rational surfaces. We show that to every such sequence one can associate a smooth complete toric surface in a canonical way. We use this structural…

Algebraic Geometry · Mathematics 2019-02-20 Lutz Hille , Markus Perling

We show that complex Fano hypersurfaces can have arbitrarily large degrees of irrationality. More precisely, if we fix a Fano index e, then the degree of irrationality of a very general complex Fano hypersurface of index e and dimension n…

Algebraic Geometry · Mathematics 2021-11-11 Nathan Chen , David Stapleton

We show the existence of metrically dense entire curves in rationally connected complex projective manifolds confirming for this case a conjecture according to which such entire curves on projective manifolds exist if and only if these are…

Algebraic Geometry · Mathematics 2020-01-09 Frederic Campana , Joerg Winkelmann

We study Fano schemes $F_k(X)$ for complete intersections $X$ in a projective toric variety $Y\subset \mathbb{P}^n$. Our strategy is to decompose $F_k(X)$ into closed subschemes based on the irreducible decomposition of $F_k(Y)$ as studied…

Algebraic Geometry · Mathematics 2021-06-22 Nathan Ilten , Tyler L. Kelly

The main result is that a quasi-projective surface has negative log Kodaira dimension (i.e. no log pluricanonical sections) iff it is dominated by images of the affine line. This follows from our main intermediate result, that the smooth…

alg-geom · Mathematics 2008-02-03 Sean Keel , James McKernan

For Fano-Mori fibre spaces $\pi\colon V\to S$, every fibre of which is a primitive Fano variety with the global canonical threshold at least 1, and which are stable with respect to birational modifications of the base and sufficiently…

Algebraic Geometry · Mathematics 2023-11-21 Aleksandr V. Pukhlikov

In dimension two, we reduce the classification problem for asymptotically log Fano pairs to the problem of determining generality conditions on certain blow-ups. In any dimension, we prove the rationality of the body of ample angles of an…

Algebraic Geometry · Mathematics 2024-11-20 Paolo Cascini , Jesus Martinez-Garcia , Yanir A. Rubinstein

In this paper, we investigate Fano manifolds whose Chern characters satisfy some positivity conditions. We prove that such manifolds admit long chains of higher order minimal families of rational curves and are covered by higher rational…

Algebraic Geometry · Mathematics 2024-07-19 Taku Suzuki

We show that Fano lattice polygons define a class of balanced quivers with interesting properties. The combinatorics of these quivers is related to singularities of the underlying toric Fano surface. This allows us to show that every Fano…

Algebraic Geometry · Mathematics 2019-07-23 Mohammad E. Akhtar

A complete set of the Virasoro and W-constraints for the Kontsevich-Penner model, which conjecturally describes intersections on moduli spaces of open curves, was derived in our previous work. Here we show that these constraints can be…

Mathematical Physics · Physics 2017-09-13 Alexander Alexandrov

We prove that every curve on a rationally connected variety is algebraically equivalent to a (non-effective) integral sum of rational curves.

Algebraic Geometry · Mathematics 2015-02-23 Hong R. Zong

Given a Fano variety $Y$ and a simple normal crossings divisor $D\subseteq Y$ which is anti-canonical, we prove a formula relating counts of discs with boundary on a Lagrangian $L\subseteq Y\backslash D$ to counts of rational curves in $Y$,…

Symplectic Geometry · Mathematics 2023-05-04 Mohamed El Alami

We study rational curves on algebraic varieties, especially on normal affine varieties endowed with a $\C^*$-action. For varieties with an isolated singularity, we show that the presence of sufficiently many rational curves outside the…

Algebraic Geometry · Mathematics 2007-05-23 Hubert Flenner , Mikhail Zaidenberg

We show that for a Zariski general hypersurface $V$ of degree $M+1$ in ${\mathbb P}^{M+1}$ for $M\geqslant 5$ there are no Galois rational covers $X\dashrightarrow V$ of degree $d\geqslant 2$ with an abelian Galois group, where $X$ is a…

Algebraic Geometry · Mathematics 2024-04-17 Aleksandr V. Pukhlikov

We generalize Givental's Theorem for complete intersections in smooth toric varieties in the Fano case. In particular, we find Gromov--Witten invariants of Fano varieties of dimension $\geq 3$, which are complete intersections in weighted…

Algebraic Geometry · Mathematics 2018-08-07 Victor Przyjalkowski

In this paper, we show that projective globally $F$-regular threefolds, defined over an algebraically closed field of characteristic $p\geq 11$, are rationally chain connected.

Algebraic Geometry · Mathematics 2015-05-19 Yoshinori Gongyo , Zhiyuan Li , Zsolt Patakfalvi , Karl Schwede , Hiromu Tanaka , Hong R. Zong

It is a well-known fact that families of minimal rational curves on rational homogeneous manifolds of Picard number one are uniform, in the sense that the tangent bundle to the manifold has the same splitting type on each curve of the…

Algebraic Geometry · Mathematics 2015-11-12 Gianluca Occhetta , Luis E. Solá Conde , Kiwamu Watanabe

Chains of minimal degree rational curves have been used as an important tool in the study of Fano manifolds. Their own geometric properties, however, have not been studied much. The goal of the paper is to introduce an infinitesimal method…

Algebraic Geometry · Mathematics 2007-05-23 Jun-Muk Hwang , Stefan Kebekus

We show that every smooth projective curve over a finite field k admits a finite tame morphism to the projective line over k. Furthermore, we construct a curve with no such map when k is an infinite perfect field of characteristic two. Our…

Algebraic Geometry · Mathematics 2021-10-05 Kiran S. Kedlaya , Daniel Litt , Jakub Witaszek

We describe the families of minimal rational curves on any complete symmetric variety, and the corresponding varieties of minimal rational tangents (VMRT). In particular, we prove that these varieties are homogeneous and that for…

Algebraic Geometry · Mathematics 2025-05-20 Michel Brion , Shin-young Kim , Nicolas Perrin