scholarly journals Codimension one Fano distributions on Fano manifolds

2018 ◽  
Vol 20 (05) ◽  
pp. 1750058 ◽  
Author(s):  
Carolina Araujo ◽  
Mauricio Corrêa ◽  
Alex Massarenti
Keyword(s):  
Moduli Spaces ◽  
Projective Spaces ◽  
Complete Intersections ◽  
Picard Number ◽  
Contact Manifolds ◽  
Fano Manifolds ◽  
Codimension One ◽  
Linear Sections ◽  
Del Pezzo

In this paper, we investigate codimension one Fano distributions on Fano manifolds with Picard number one. We classify Fano distributions of maximal index on complete intersections in weighted projective spaces, Fano contact manifolds, Grassmannians of lines and their linear sections, and describe their moduli spaces. As a consequence, we obtain a classification of codimension one del Pezzo distributions on Fano manifolds with Picard number one.

scholarly journals Quotients of del Pezzo surfaces

2019 ◽  
Vol 30 (12) ◽  
pp. 1950068
Author(s):  
Andrey Trepalin
Keyword(s):  
Complete Classification ◽  
Finite Subgroup ◽  
Del Pezzo Surfaces ◽  
Picard Number ◽  
Del Pezzo Surface ◽  
Cyclic Groups ◽  
Trivial Group ◽  
Quotient Surface ◽  
Del Pezzo

Let [Formula: see text] be any field of characteristic zero, [Formula: see text] be a del Pezzo surface and [Formula: see text] be a finite subgroup in [Formula: see text]. In this paper, we study when the quotient surface [Formula: see text] can be non-rational over [Formula: see text]. Obviously, if there are no smooth [Formula: see text]-points on [Formula: see text] then it is not [Formula: see text]-rational. Therefore, under assumption that the set of smooth [Formula: see text]-points on [Formula: see text] is not empty we show that there are few possibilities for non-[Formula: see text]-rational quotients. The quotients of del Pezzo surfaces of degree [Formula: see text] and greater are considered in the author’s previous papers. In this paper, we study the quotients of del Pezzo surfaces of degree [Formula: see text]. We show that they can be non-[Formula: see text]-rational only for the trivial group or cyclic groups of order [Formula: see text], [Formula: see text] and [Formula: see text]. For the trivial group and the group of order [Formula: see text], we show that both [Formula: see text] and [Formula: see text] are not [Formula: see text]-rational if the [Formula: see text]-invariant Picard number of [Formula: see text] is [Formula: see text]. For the groups of order [Formula: see text] and [Formula: see text], we construct examples of both [Formula: see text]-rational and non-[Formula: see text]-rational quotients of both [Formula: see text]-rational and non-[Formula: see text]-rational del Pezzo surfaces of degree [Formula: see text] such that the [Formula: see text]-invariant Picard number of [Formula: see text] is [Formula: see text]. As a result of complete classification of non-[Formula: see text]-rational quotients of del Pezzo surfaces we classify surfaces that are birationally equivalent to quotients of [Formula: see text]-rational surfaces, and obtain some corollaries concerning fields of invariants of [Formula: see text].

scholarly journals Varieties with quadratic entry locus, II

2008 ◽  
Vol 144 (4) ◽  
pp. 949-962 ◽  
Author(s):  
Paltin Ionescu ◽  
Francesco Russo
Keyword(s):  
Hyperplane Section ◽  
Picard Group ◽  
High Index ◽  
Homogeneous Manifolds ◽  
Fano Manifolds ◽  
Linear Sections ◽  
Dual Defective

AbstractWe continue the study, begun in [F. Russo, Varieties with quadratic entry locus. I, Preprint (2006), math. AG/0701889] , of secant defective manifolds having ‘simple entry loci’. We prove that such manifolds are rational and describe them in terms of tangential projections. Using also the work of [P. Ionescu and F. Russo, Conic-connected manifolds, Preprint (2006), math. AG/0701885], their classification is reduced to the case of Fano manifolds of high index, whose Picard group is generated by the hyperplane section class. Conjecturally, the former should be linear sections of rational homogeneous manifolds. We also provide evidence that the classification of linearly normal dual defective manifolds with Picard group generated by the hyperplane section should follow along the same lines.

Varieties with nef diagonal

2019 ◽  
Vol 31 (02) ◽  
pp. 2050011 ◽  
Author(s):  
Taku Suzuki ◽  
Kiwamu Watanabe
Keyword(s):  
Projective Variety ◽  
Smooth Projective Variety ◽  
Complete Intersections ◽  
Spherical Varieties ◽  
Del Pezzo

For a smooth projective variety [Formula: see text], we consider when the diagonal [Formula: see text] is nef as a cycle on [Formula: see text]. In particular, we give a classification of complete intersections and smooth del Pezzo varieties where the diagonal is nef. We also study the nefness of the diagonal for spherical varieties.

scholarly journals Stable Rationality of Cyclic Covers of Projective Spaces

2019 ◽  
Vol 62 (3) ◽  
pp. 667-682 ◽  
Author(s):  
Takuzo Okada
Keyword(s):  
Projective Spaces ◽  
Complete Intersections ◽  
Cyclic Cover ◽  
Fano Manifolds ◽  
Stable Rationality ◽  
Cyclic Covers

AbstractThe main aim of this paper is to show that a cyclic cover of ℙn branched along a very general divisor of degree d is not stably rational, provided that n ≥ 3 and d ≥ n + 1. This generalizes the result of Colliot-Thélène and Pirutka. Generalizations for cyclic covers over complete intersections and applications to suitable Fano manifolds are also discussed.

scholarly journals Fano manifolds containing a negative divisor isomorphic to a rational homogeneous space of Picard number one

2020 ◽  
Vol 31 (09) ◽  
pp. 2050066
Author(s):  
Jie Liu
Keyword(s):  
Homogeneous Space ◽  
Complete Classification ◽  
Picard Number ◽  
Fano Manifold ◽  
Fano Manifolds ◽  
Conormal Bundle ◽  
Rational Homogeneous Space

Let [Formula: see text] be an [Formula: see text]-dimensional complex Fano manifold [Formula: see text]. Assume that [Formula: see text] contains a divisor [Formula: see text], which is isomorphic to a rational homogeneous space with Picard number one, such that the conormal bundle [Formula: see text] is ample over [Formula: see text]. Building on the works of Tsukioka, Watanabe and Casagrande–Druel, we give a complete classification of such pairs [Formula: see text].

Examples of K-Unstable Fano Manifolds with the Picard Number 1

2017 ◽  
Vol 60 (4) ◽  
pp. 881-891 ◽  
Author(s):  
Kento Fujita
Keyword(s):  
Picard Number ◽  
Fano Manifolds ◽  
Del Pezzo

AbstractWe show that the pair (X, –KX) is K-unstable for a del Pezzo manifold X of degree 5 with dimension 4 or 5. This disproves a conjecture of Odaka and Okada.

scholarly journals Rank two aCM bundles on the del Pezzo threefold with Picard number 3

2015 ◽  
Vol 429 ◽  
pp. 413-446 ◽  
Author(s):  
Gianfranco Casnati ◽  
Daniele Faenzi ◽  
Francesco Malaspina
Keyword(s):  
Picard Number ◽  
Del Pezzo ◽  
Acm Bundles

scholarly journals Affine cones over cubic surfaces are flexible in codimension one

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Alexander Perepechko
Keyword(s):  
Automorphism Group ◽  
Open Subset ◽  
Pezzo Surface ◽  
Ample Divisor ◽  
Transitive Action ◽  
Del Pezzo Surface ◽  
Codimension One ◽  
Cubic Surfaces ◽  
Special Automorphism ◽  
Del Pezzo

AbstractLet Y be a smooth del Pezzo surface of degree 3 polarized by a very ample divisor that is not proportional to the anticanonical one. Then the affine cone over Y is flexible in codimension one. Equivalently, such a cone has an open subset with an infinitely transitive action of the special automorphism group on it.

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