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Using a construction due to C. Casagrande and further developed by the author, we prove that the Picard number of a non-smooth Fano 3-fold with isolated factorial canonical singularities, is at most 6.

Algebraic Geometry · Mathematics 2013-01-14 Gloria Della Noce

As a generalization of the Mukai conjecture, we conjecture that the Fano manifolds $X$ which satisfy the property $\rho_X(r_X-1)\geq\dim X-1$ have very special structure, where $\rho_X$ is the Picard number of $X$ and $r_X$ is the index of…

Algebraic Geometry · Mathematics 2015-04-03 Kento Fujita

The Picard number of a Fano manifold X obtained by blowing up a curve in a smooth projective variety is known to be at most 5, in any dimension greater than or equal to 4. We show that the Picard number attains to the maximal if and only if…

Algebraic Geometry · Mathematics 2009-04-16 Toru Tsukioka

Let $X$, $Y$ be Fano threefolds of Picard number one and such that the ample generators of Picard groups are very ample. Let $X$ be of index one and $Y$ be of index two. It is shown that the only morphisms from $X$ to $Y$ are double…

Algebraic Geometry · Mathematics 2007-05-23 Ekaterina Amerik

We study the varieties of reductions associated to the variety of rank one matrices in $\fgl\_n$. These varieties are defined as natural compactifications of the different ways to write the identity matrix as a sum of $n$ rank one matrices.…

Algebraic Geometry · Mathematics 2008-10-15 Atanas Iliev , Laurent Manivel

We classify nonrational Fano threefolds $X$ with terminal Gorenstein singularities such that $\mathrm{\rk}\, \mathrm{\Pic}(X)=1$, $(-K_X)^3\ge 8$, and $\mathrm{\rk}\, \mathrm{\Cl}(X)\le 2$.

Algebraic Geometry · Mathematics 2022-05-18 Yuri Prokhorov

We study fibers with isolated singularities of Landau-Ginzburg models for Fano threefolds of Picard rank one. We compare the data we get with maximal known lengths of exceptional collections in derived categories of coherent sheaves on the…

Algebraic Geometry · Mathematics 2026-01-26 Victor Przyjalkowski

We study smoothings of Fano threefolds. We prove that the Picard number remains constant in the case of terminal Gorenstein singularities.

Algebraic Geometry · Mathematics 2007-05-23 Priska Jahnke , Ivo Radloff

We construct 4 di erent families of smooth Fano fourfolds with Picard rank 1, which contain cylinders, i.e., Zariski open subsets of the form Z x A1, where Z is a quasiprojective variety. The affi ne cones over such a fourfold admit eff…

Algebraic Geometry · Mathematics 2014-06-25 Yuri Prokhorov , Mikhail Zaidenberg

In this paper, we prove various results on boundedness and singularities of Fano fibrations and of Fano type fibrations. A Fano fibration is a projective morphism $X\to Z$ of algebraic varieties with connected fibres such that $X$ is Fano…

Algebraic Geometry · Mathematics 2022-09-20 Caucher Birkar

Let $X$ be a complex smooth Fano variety of dimension $n$. Assume that $X$ admits a birational contraction of an extremal ray. In this paper, we give a classification of such $X$ when the pseudoindex is equal to $\frac{\dim X}{2}$.

Algebraic Geometry · Mathematics 2025-10-22 Kiwamu Watanabe

In this paper we study mildly singular del Pezzo foliations on complex projective manifolds with Picard number one

Algebraic Geometry · Mathematics 2014-09-16 Carolina Araujo , Stéphane Druel

We show that every Mori dream space of globally $F$-regular type is of Fano type. As an application, we give a characterization of varieties of Fano type in terms of the singularities of their Cox rings.

Algebraic Geometry · Mathematics 2012-01-06 Yoshinori Gongyo , Shinnosuke Okawa , Akiyoshi Sannai , Shunsuke Takagi

Fano varieties are subvarieties of the Grassmannian whose points parametrize linear subspaces contained in a given projective variety. These expository notes give an account of results on Fano varieties of complete intersections, with a…

Algebraic Geometry · Mathematics 2012-12-05 Paul Larsen

We show that being a general fibre of a Mori fibre space is a rather restrictive condition for a Fano variety. More specifically, we obtain two criteria (one sufficient and one necessary) for a Q-factorial Fano variety with terminal…

Algebraic Geometry · Mathematics 2016-06-09 Giulio Codogni , Andrea Fanelli , Roberto Svaldi , Luca Tasin

In this paper we show that a general element of $|-K_X|$ on a four-dimensional Fano manifold has at most terminal singularities. We then determine an explicit local expression of these singular points.

Algebraic Geometry · Mathematics 2015-05-12 Liana Heuberger

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…

Algebraic Geometry · Mathematics 2007-09-21 Elena Chierici , Gianluca Occhetta

It is shown that hypersurfaces of degree $M$ in ${\mathbb P}^M$, $M\geqslant 5$, with at most quadratic singularities of rank at least 3, satisfying certain conditions of general position, are birationally superrigid Fano varieties and the…

Algebraic Geometry · Mathematics 2023-12-29 Aleksandr V. Pukhlikov

We give a complete classification of smooth, complex projective Fano 4-folds of Picard number 3 having a prime divisor of Picard number 1. They form 28 distinct families, and we compute the main numerical invariants, study the base locus of…

Algebraic Geometry · Mathematics 2023-03-24 Saverio Andrea Secci

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
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