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We construct first examples of Fano varieties with torsion in their third cohomology group. The examples are constructed as double covers of linear sections of rank loci of symmetric matrices, and can be seen as higher-dimensional analogues…

代数几何 · 数学 2023-11-17 John Christian Ottem , Jørgen Vold Rennemo

We study the enumerativity of Gromov-Witten invariants where the domain curve is fixed in moduli and required to pass through the maximum possible number of points. We say a Fano manifold satisfies asymptotic enumerativity if such…

代数几何 · 数学 2024-12-04 Roya Beheshti , Brian Lehmann , Carl Lian , Eric Riedl , Jason Starr , Sho Tanimoto

Let X be a Fano manifold of pseudoindex i_X whose Picard number is at least two and let R be an extremal ray of X with exceptional locus Exc(R). We prove an inequality which bounds the length of R in terms of i_X and of the dimension of…

代数几何 · 数学 2007-05-23 Marco Andreatta , Gianluca Occhetta

We classify some special classes of non-rational Fano threefolds with terminal singularities. In particular, all such hyperelliptic and trigonal varieties are found.

代数几何 · 数学 2019-07-15 Yuri Prokhorov

By a result of Mukai, the non-abelian Brill-Noether locus X = M_C(2,K:3F) of type II, defined by a stable rank 2 vector bundle F of invariant 3 over a plane quartic curve C, is a prime Fano 3-fold X of degree 16. The associate ruled surface…

代数几何 · 数学 2007-05-23 Atanas Iliev

We prove an optimal Kawamata-Miyaoka-type inequality for terminal $\mathbb Q$-Fano threefolds with Fano index at least $3$. As an application, any terminal $\mathbb Q$-Fano threefold $X$ satisfies the following Kawamata-Miyaoka-type…

代数几何 · 数学 2026-05-27 Haidong Liu , Jie Liu

We show that a general prime Fano threefold X of genus 8 can be reconstructed from the pair $(\Gamma,L)$, where $\Gamma$ is its Fano curve of lines and $L=O_{\Gamma}(1)$ is the theta-characteristic which gives a natural embedding $\Gamma…

代数几何 · 数学 2010-05-14 Flaminio Flamini , Edoardo Sernesi

We show that the global log canonical threshold of generic Fano complete intersections of index 1 and codimension $k$ in ${\mathbb P}^{M+k}$ is equal to 1 if $M\geqslant 3k+4$ and the highest degree of defining equations is at least 8. This…

代数几何 · 数学 2014-12-17 Thomas Eckl , Aleksandr Pukhlikov

We introduce the notion of infinitesimal variations of mixed Hodge structures and invariants associated to them. We describe these invariants in the case of a pair $(X,Y)$ with $X$ a Fano 3-fold and $Y$ a smooth anticanonical K3 surface and…

代数几何 · 数学 2024-06-26 Rodolfo Aguilar , Mark Green , Phillip Griffiths

We give new proofs of the K-polystability of two smooth Fano threefolds. One of them is a~smooth divisor in $\mathbb{P}^1\times\mathbb{P}^1\times\mathbb{P}^2$ of degree $(1,1,1)$, which is unique up to isomorphism. Another one is the~blow…

代数几何 · 数学 2021-07-13 Ivan Cheltsov , Hendrik Süß

The purpose of this note is to provide yet another example of the link between certain conformal geometries and ordinary differential equations, along the lines of the examples discussed by Nurowski in math.DG/0406400. In this particular…

微分几何 · 数学 2008-01-01 Robert L. Bryant

We study the relation between the coregularity, the index of log Calabi-Yau pairs, and the complements of Fano varieties. We show that the index of a log Calabi-Yau pair $(X,B)$ of coregularity $1$ is at most $120\lambda^2$, where $\lambda$…

代数几何 · 数学 2025-02-12 Fernando Figueroa , Stefano Filipazzi , Joaquín Moraga , Junyao Peng

We prove that the deformations of a smooth complex Fano threefold X with Picard number 1, index 1, and degree 10, are unobstructed. The differential of the period map has two-dimensional kernel. We construct two two-dimensional components…

代数几何 · 数学 2008-12-22 O. Debarre , A. Iliev , L. Manivel

Let X be a complex Fano manifold of dimension n. Let s(X) be the sum of l(R)-1 for all the extremal rays of X, the edges of the cone NE(X) of curves of X, where l(R) denotes the minimum of (-K_X \cdot C) for all rational curves C whose…

代数几何 · 数学 2013-10-01 Kento Fujita

We study the Hilbert scheme $\mathcal{H}$ of twisted cubics on a special smooth Gushel-Mukai threefolds $X_{10}$. We show that it is a smooth irreducible projective threefold if $X_{10}$ is general among special Gushel-Mukai threefolds,…

代数几何 · 数学 2021-08-30 Shizhuo Zhang

We study the symplectic resolution of the Fano variety of lines on some singular cyclic cubic fourfolds, i.e. cubic fourfolds arising as cyclic 3:1 cover of $\mathbb{P}^4$ branched along a cubic threefold. In particular we are interested in…

代数几何 · 数学 2023-12-27 Samuel Boissière , Paola Comparin , Lucas Li Bassi

In this article, we determine all equivariant compactifications of the three-dimensional vector group $\mathbf{G}_a^3$ which are smooth Fano threefolds with Picard number greater or equal than two.

代数几何 · 数学 2019-12-20 Zhizhong Huang , Pedro Montero

We study Fano manifolds of pseudoindex greater than one and dimension greater than five, which are blow-ups of smooth varieties along smooth centers of dimension equal to the pseudoindex of the manifold. We obtain a classification of the…

代数几何 · 数学 2007-09-21 Elena Chierici , Gianluca Occhetta

In this paper, we give a partial affirmative answer to the BAB conjecture for $3$-folds in characteristic $p>5$. Specifically, we prove that a set $\mathcal{D}$ of weak Fano $3$-folds over an uncountable algebraically closed field is…

代数几何 · 数学 2024-03-06 Kenta Sato

Mukai varieties are Fano varieties of Picard number one and coindex three. In genus seven to ten they are linear sections of some special homogeneous varieties. We describe the generic automorphism groups of these varieties. When they are…

代数几何 · 数学 2022-02-01 Thomas Dedieu , Laurent Manivel