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Let $X$ be an $n$-dimensional complex Fano manifolds $(n\geq 3)$. Assume that $X$ contains a divisor $A$, which is isomorphic to a rational homogeneous space with Picard number one, such that the conormal bundle $\mathscr{N}^*_{A/X}$ is…

Algebraic Geometry · Mathematics 2021-07-30 Jie Liu

We consider projective Hyper-K\"ahler manifolds of dimension four that are deformation equivalent to Hilbert squares of K3 surfaces. In case such a manifold admits a divisorial contraction, the exceptional divisor is a conic bundle over a…

Algebraic Geometry · Mathematics 2025-04-07 Federica Galluzzi , Bert Van Geemen

We classify birationally rigid orbifold Fano 3-folds of index one defined by $5 \times 5$ Pfaffians. We give a sharp criterion for birational rigidity of these families based on the type of singularities that the varieties admit. Various…

Algebraic Geometry · Mathematics 2022-07-22 Hamid Abban , Takuzo Okada

A projective log variety (X, D) is called "a log Fano manifold" if X is smooth and if D is a reduced simple normal crossing divisor on X with -(K_X+D) ample. The n-dimensional log Fano manifolds (X, D) with nonzero D are classified in this…

Algebraic Geometry · Mathematics 2015-01-14 Kento Fujita

We classify Fano threefolds with only terminal singularities whose canonical class is Cartier and divisible by 2, and satisfying an additional assumption that the $G$-invariant part of the Weil divisor class group is of rank 1 with respect…

Algebraic Geometry · Mathematics 2013-08-06 Yuri Prokhorov

In this paper, we classify Fano fourfolds whose the second exterior power of tangent bundles are numerically effective with Picard number greater than one.

Algebraic Geometry · Mathematics 2014-01-14 Kazunori Yasutake

We construct some new deformation families of four-dimensional Fano manifolds of index $1$ in some known classes of Gorenstein formats. These families have explicit descriptions in terms of equations, defining their image under the…

Algebraic Geometry · Mathematics 2021-07-09 Muhammad Imran Qureshi

We study smooth complex projective polarized varieties $(X,H)$ of dimension $ n \ge 2$ which admit a dominating family $V$ of rational curves of $H$-degree $3$, such that two general points of $X$ may be joined by a curve parametrized by…

Algebraic Geometry · Mathematics 2010-09-21 Gianluca Occhetta , Valentina Paterno

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…

Algebraic Geometry · Mathematics 2013-10-01 Kento Fujita

We construct new families of smooth Fano fourfolds with Picard rank 1, which contain cylinders, i.e., Zariski open subsets of form $Z\times A^1$, where $Z$ is a quasiprojective variety. The affine cones over such a fourfold admit effective…

Algebraic Geometry · Mathematics 2015-07-08 Yuri Prokhorov , Mikhail Zaidenberg

For a general cubic fourfold $X \subset \mathbb{P}^5$, we compute the Hodge numbers of the locus $S \subset F$ of lines of second type. We also give an upper bound of 6 for the degree of irrationality of the Fano scheme of lines of any…

Algebraic Geometry · Mathematics 2023-09-07 Frank Gounelas , Alexis Kouvidakis

In this paper, we prove a special case of Campana--Peternell's conjecture in dimension 4. Specifically, we show that a projective smooth fourfold $X$ with $c^2_1(X)\cdot c_2(X)\neq 0$ and strictly nef anti-canonical divisor $-K_X$ is a Fano…

Algebraic Geometry · Mathematics 2023-05-10 Haidong Liu

We classify the cones of curves of Fano varieties of dimension greater or equal than five and (pseudo)index dim X -3, describing the number and type of their extremal rays.

Algebraic Geometry · Mathematics 2017-09-29 Elena Chierici , Gianluca Occhetta

In this paper we extend to the singular setting the theory of Fano foliations developed in our previous paper. A Q-Fano foliation on a complex projective variety X is a foliation F whose anti-canonical class is an ample Q-Cartier divisor.…

Algebraic Geometry · Mathematics 2014-04-16 Carolina Araujo , Stéphane Druel

We study a particular kind of fiber type contractions between complex, projective, smooth varieties f:X->Y, called Fano conic bundles. This means that X is a Fano variety, and every fiber of f is isomorphic to a plane conic. Denoting by…

Algebraic Geometry · Mathematics 2018-03-15 Eleonora Anna Romano

In this paper we address Fano manifolds X with a locally unsplit dominating family of rational curves of anticanonical degree equal to the dimension of X. We first observe that their Picard number is at most 3, and then we provide a…

Algebraic Geometry · Mathematics 2015-01-12 Cinzia Casagrande , Stéphane Druel

Curves of low genus on a surface carry important informations on that surface. We study the Fano surfaces of lines of cubic threefolds that contain 12 or 30 elliptic curves. We determine their Picard number and compute a basis of the…

Algebraic Geometry · Mathematics 2010-02-05 Xavier Roulleau

In this paper, an update on the classification of smooth weak Fano threefolds with Picard number two and small anti-canonical maps is given. Geometric constructions are provided for previously open numerical cases by blowing up certain…

Algebraic Geometry · Mathematics 2025-01-22 Joseph Cutrone , Nicholas Marshburn

We prove that a smooth projective variety $X$ of dimension $n$ with strictly nef third, fourth or $(n-1)$-th exterior power of the tangent bundle is a Fano variety. Moreover, in the first two cases, we provide a classification for $X$ under…

Algebraic Geometry · Mathematics 2024-12-13 Cécile Gachet

The cohomological rigidity problem for toric manifolds asks whether toric manifolds are diffeomorphic (or homeomorphic) if their integral cohomology rings are isomorphic. Many affirmative partial solutions to the problem have been obtained…

Algebraic Topology · Mathematics 2020-05-29 Akihiro Higashitani , Kazuki Kurimoto , Mikiya Masuda