Takeru Fukuoka, Wahei Hara, Daizo Ishikawa
We classify rank two vector bundles on a given del Pezzo threefold of degree four whose projectivizations are weak Fano into seven cases. We also give an example for each of these seven cases.
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We prove that very general non-rational Fano threefolds which are not birational to cubic threefolds are not stably rational.
In this paper we classify nodal rational non-$\mathbb{Q}$-factorial del Pezzo threefolds of degree 2 which can be $G$-birationally rigid for some subgroup $G\subset \operatorname{Aut}(X)$.
We consider certain elliptic threefolds over the projective plane (more generally over certain rational surfaces) with a section in Weierstrass normal form. In particular, over a del Pezzo surface of degree 8, these elliptic threefolds are Calabi-Yau threefolds. We will discuss especially the generating functions of Gromov-Witten and Gopakumar-Vafa invariants.
Using the geometry of an almost del Pezzo threefold, we show that the moduli space of genus $g$ one-pointed ineffective spin hyperelliptic curves is rational for every $g\geq 2$.
Derived categories of nodal del Pezzo threefolds
本文完整回答了结点del Pezzo三维簇导出范畴的Kawamata型半正交分解存在性问题，证明了度数1至4无此分解而度数5存在，并利用从直线的投影构造了度数5的分解。
By Jahnke-Peternell-Radloff and Takeuchi, almost Fano threefolds with del Pezzo fibrations were classified. Among them, there exists 10 classes such that the existence of members of these was not proved. In this paper, we construct such examples belonging to each of 10 classes.
We prove the irreducibility of moduli spaces of rational curves on a general del Pezzo threefold of Picard rank $1$ and degree $1$. As corollaries, we confirm Geometric Manin's conjecture and enumerativity of certain Gromov-Witten invariants for these threefolds.
We refine the classification of weak Fano threefolds with sextic del Pezzo fibrations by considering the Hodge numbers of them. By the refined classification result, such threefolds are classified into 17 cases. The main result of this paper is to show that there exists an example for each of 17 cases, except for 2 cases.
Quintic del Pezzo threefolds in positive and mixed characteristic
该研究对任意基概形上的光滑五次del Pezzo三重曲面进行分类，描述其相关几何结构并发现特征2下的新现象，还给出Shafarevich猜想的精细化及整数环上的同构类结果。
We study the syzygetic structure of projections of del Pezzo surfaces in order to construct singular Calabi-Yau threefolds. By smoothing those threefolds, we obtain new examples of Calabi-Yau threefolds with Picard group of rank 1. We also give an example of type II primitive contraction whose exceptional divisor is the blow-up of the projective plane at a point.
This article treats smooth weak Fano 3-folds having an extremal ray of type D. Smooth weak Fano 3-folds with an extremal ray of type D except of degree 6 are classified into 47 deformation types.
Nodal quintic del Pezzo threefolds and their derived categories
本文为节点五次 del Pezzo 三维簇构造川又型半正交分解，将其导出范畴分解为有限维代数的导出范畴，通过双有理映射到二次曲面纤维化实现。
Motivated by the general question of existence of open A1-cylinders in higher dimensional pro-jective varieties, we consider the case of Mori Fiber Spaces of relative dimension three, whose general closed fibers are isomorphic to the quintic del Pezzo threefold V5 , the smooth Fano threefold of index two and degree five. We show that the total spaces of these Mori Fiber Spaces always contain relative A2-cylinders, and we characterize those admitting relative A3-cylinders in terms of the existence of certain special lines in their generic fibers.
Rank two weak Fano bundles on del Pezzo threefolds of degree five
本文分类了五次del Pezzo三维流形上射影化为弱Fano的秩二向量丛，据此刻画其模空间的光滑性、不可约性与精细性，并推广到Picard秩为1的情形。
We prove a criterion of nonsingularity of a complete intersection of two fiberwise quadrics in a scroll over $P^1$. As a corollary we derive the following addition to the Alexeev theorem on rationality of standard Del Pezzo fibrations of degree 4 over $P^1$: we prove that any fibration of this kind with the topological Euler characteristic -4 is rational.
We study the Fano surface S of the Fermat cubic threefold. We prove that S is a degree 81 abelian cover of the degree 5 del Pezzo surface and that the complement of the union of 12 disjoint elliptic curves on S is a ball quotient. The lattice of this ball quotient is related to the Deligne-Mostow lattice number 1.
Moduli space of genus one curves on quartic and quintic del Pezzo threefolds
本文研究四次和五次 del Pezzo 三维簇上光滑亏格一曲线的空间，描述了 Kontsevich 模空间的不可约分支并分类了从一般椭圆曲线出发的态射空间，验证了复数域上所有四次和五次 del Pezzo 三维簇的几何 Manin 猜想。
This is the fourth of a series of papers studying real algebraic threefolds, but the methods are mostly independent from the previous ones. Let $f:X\to C$ be a map of a smooth projective real algebraic 3-fold to a curve $C$ whose general fibers are rational surfaces. Assume that the set of real points of $X$ is an orientable 3-manifold $M$. The aim of the paper is to give a topological description of $M$.
We study certain pencils of del Pezzo surfaces generated by a smooth del Pezzo surface S of degree less or equal to 3 anti-canonically embedded into a weighted projective space P and an appropriate multiple of a hyperplane H. Our main observation is that every minimal model program relative to the morphism lifting such pencil on a suitable resolution of its indeterminacies preserves the open subset P H â A^3. As an application, we obtain projective completions of A^3 into del Pezzo fibrations over P^1 of every degree less or equal to 4. We also obtain completions of A^3 into Mori conic bundles…
We classify indecomposable aCM bundles of rank $2$ on the del Pezzo threefold of degree $7$ and analyze the corresponding moduli spaces.
Quartic curves in the quintic del Pezzo threefold
本文证明五次 del Pezzo 三维簇 X5 上有理四次曲线的 Hilbert 概形 H4(X5) 同构于 X5 上直线的 Hilbert 概形上的 Grassmannian 丛，因此光滑且不可约。
Ulrich bundles on Del Pezzo threefolds
本文研究光滑 Fano 三重流形上稳定 Ulrich 丛的模空间，证明了指数为二时任意秩及指数为四时偶秩情形的光滑性与维数公式，并给出一般射影三重流形上 Ulrich 丛存在的充要条件。
Let k be an algebraically closed field of characteristic 0. A del Pezzo threefold F with maximal Picard number is isomorphic to P^1xP^1xP^1, where P^1 is the projective line over k. In the present paper we completely classify locally free sheaves of rank 2 with vanishing intermediate cohomology over such an F. Such a classification extends similar results proved by E. Arrondo and L. Costa regarding del Pezzo threefolds with Picard number 1.
Derived categories of Fano threefolds and degenerations
本文利用奇点的范畴吸收技术，证明了特定度数德尔佩佐三维簇导出范畴非平凡分支及相关分解可光滑形变至对应亏格素法诺三维簇导出范畴非平凡分支，修正并证明了相关猜想，还描述了模空间紧化及边界分支。
Resonance, syzygies, and rank-$3$ Ulrich bundles on the del Pezzo threefold $V_5$
本文研究了在del Pezzo三维流形V_5上，通过乌里奇向量包的截面零点描述亏格14、次数18的曲线的几何条件，并探讨了其与特殊秩2向量包的共振关系，以及曲线唯一性结论。
We prove the existence of Kahler-Einstein metrics on a nonsingular section of the Grassmannian $\mathrm{Gr}(2, 5)\subset\mathbb{P}^9$ by a linear subspace of codimension 3, and the Fermat hypersurface of degree 6 in $\mathbb{P}(1,1,1,2,3)$. We also show that a global log canonical threshold of the Mukai--Umemura variety is equal to 1/2.
In this paper, we investigate quotients of Calabi-Yau manifolds Y embedded in Fano varieties X which are products of two del Pezzo surfaces - with respect to groups G that act freely on Y. In particular, we revisit some known examples and we obtain some new Calabi-Yau varieties with small Hodge numbers. The groups G are subgroups of the automorphism group of X, which is described in terms of the automorphism group of the two del Pezzo surfaces.
New perspectives on categorical Torelli theorems for del Pezzo threefolds
本文通过 Brill-Noether 重构和 Fourier-Mukai 型等价提升两种视角研究 del Pezzo 三重流形的 Kuznetsov 分量，完整刻画其自等价群，并给出 Kuznetsov Fano 三重流形猜想的新反证。
We consider threefold del Pezzo fibrations over a curve germ whose central fiber is non-rational. Under the additional assumption that the singularities of the total space are at worst ordinary double points, we apply a suitable base change and show that there is a 1-to-1 correpspondence between such fibrations and certain non-singular del Pezzo fibrations equipped with a cyclic group action.
We construct a klt del Pezzo surface in characteristic three violating the Kawamata-Viehweg vanishing theorem. As a consequence we show that there exists a Kawamata log terminal threefold singularity which is not Cohen-Macaulay in characteristic three.
In this note we illustrate the Fanosearch programme of Coates, Corti, Galkin, Golyshev, and Kasprzyk in the example of the anticanonical cone over the smooth del Pezzo surface of degree 6.
In this paper we classify all potentially G-birationally rigid del Pezzo threefolds of degree 4 and their automorphism groups and prove the G-birational rigidity of one of them
We study faithful actions with a dense orbit of abelian unipotent groups on quintic del Pezzo varieties over a field of characteristic zero. Such varieties are forms of linear sections of the Grassmannian of planes in a 5-dimensional vector space. We characterize which smooth forms admit these types of actions and show that in case of existence, the action is unique up to equivalence by automorphisms. We also give a similar classification for mildly singular quintic del Pezzo threefolds and surfaces.
Real singular Del Pezzo surfaces and threefolds fibred by rational curves, I
本文研究实光滑射影三维簇有理曲线纤维化的拓扑，证明几何有理底曲面时 Seifert 纤维化或透镜空间连通和的参数 k 不超过 4，并肯定回答 Kollár 的两个问题，通过实奇异 Del Pezzo 曲面分析得出。
We show that a del Pezzo fibration $π$ : V $\rightarrow$ W of degre d contains a vertical open cylinder, that is, an open subset whose intersection with the generic fiber of $π$ is isomorphic to $Z\times\mathbb{A}_{K}^{1}$ for some quasi-projective variety Z defined over the function field K of W , if and only if d $\ge$ 5 and $π$ : V $\rightarrow$ W admits a rational section. We also construct twisted cylinders in total spaces of threefold del Pezzo fibrations $π$ : V $\rightarrow$ P 1 of degree d $\le$ 4.
We prove the Kawamata-Viehweg vanishing theorem for surfaces of del Pezzo type over perfect fields of positive characteristic $p>5$. As a consequence, we show that klt threefold singularities over a perfect base field of characteristic $p>5$ are rational. We show that these theorems are sharp by providing counterexamples in characteristic $5$.
Relative BPS state counts for log Calabi-Yau surface pairs were introduced by Gross-Pandharipande-Siebert and conjectured by the authors to be integers. For toric Del Pezzo surfaces, we provide an arithmetic proof of this conjecture, by relating these invariants to the local BPS state counts of the surfaces. The latter were shown to be integers by Peng; and more generally for toric Calabi-Yau threefolds by Konishi.
Weak del Pezzo surfaces with irregularity
本文在非完满域上构造了非正则性q>0的正规del Pezzo曲面与正则弱del Pezzo曲面，它们是Reid分类的非正规del Pezzo曲面的扭形式，可作为带典范奇点三维簇上Fano–Mori收缩的一般纤维。
Rational curves on Fano threefolds with Gorenstein terminal singularities
本文研究具有Gorenstein终端奇点的Fano三维簇上的有理曲线，推广了几何Manin猜想至奇异情形，并证明了某些奇异del Pezzo三维簇的该猜想。
In this paper, we prove a Kawamata--Viehweg type vanishing theorem for smooth Fano threefolds, canonical del Pezzo surfaces and del Pezzo fibrations in positive characteristic.
We settle a question that originates from results and remarks by Kollár on extremal ray in the minimal model program: In positive characteristics, there are no Mori fibrations on threefolds with only terminal singularities whose generic fibers are geometrically non-normal surfaces. To show this we establish some general structure results for del Pezzo surfaces over imperfect ground fields. This relies on Reid's classification of non-normal del Pezzo surfaces over algebraically closed fields, combined with a detailed analysis of geometrical non-reducedness over imperfect fields of p-degree one.
The exceptional log Del Pezzo surfaces with delta=1 are classified.
We study del Pezzo varieties, higher-dimensional analogues of del Pezzo surfaces. In particular, we introduce ADE classification of del Pezzo varieties, show that in type A the dimension of non-conical del Pezzo varieties is bounded by $12 - d - r$, where $d$ is the degree and $r$ is the rank of the class group, and classify maximal del Pezzo varieties.
Unirational Fano threefolds
本文运用Cheltsov等人的相对阿贝尔-雅可比构造，得到50维单有理次数1德尔佩佐三维簇族，构造了两类单有理三维簇的显式单参数族，并重新阐释了双二次三维簇的Roth--Iskovskikh单有理性构造。
We prove that smooth Fano threefolds have toric Landau--Ginzburg models. More precise, we prove that their Landau--Ginzburg models, presented as Laurent polynomials, admit compactifications to families of K3 surfaces, and we describe their fibers over infinity. We also give an explicit construction of Landau--Ginzburg models for del Pezzo surfaces and any divisors on them.
We study sextic del Pezzo surface fibrations via root stacks.
We address weak approximation for certain del Pezzo surfaces defined over the function field of a curve. We study the rational connectivity of the smooth locus of degree two del Pezzo surfaces with two A1 singularities in order to prove weak approximation for degree two del Pezzo surfaces with square-free discriminant.
We classify codimension 2 well-formed and quasi-smooth weighted complete intersection del Pezzo surfaces.
In this paper, we study rigidity of nonsingular del Pezzo fibrations over a germ of smooth curve.
On the coregularity of del Pezzo surfaces with du Val singularities
研究了具有du Val奇点的del Pezzo表面的核心正则性，发现正核心正则性表面对应于具有特殊性质的非平凡椭圆纤维化，且大多数表面核心正则性为0。
We give examples of K-unstable singular del Pezzo surfaces which are weighted hypersurfaces with index 2.
We prove that a del Pezzo surface with Picard number one has at most four singular points.
We study del Pezzo fibrations of degree 1 with terminal singularities. A connection between singularities on del Pezzo surfaces of degree 1 and Kodaira's classification of elliptic singular fibers will be studied in this paper. By this investigation we obtain several results on birational maps of del Pezzo fibrations of degree 1 with terminal singularities.
We consider the problem of interpolating projective varieties through points and linear spaces. We show that del Pezzo surfaces satisfy weak interpolation.
We study irreducibility of families of degree 4 Del Pezzo surface fibrations over curves.
We discuss the rational points on del Pezzo surface of degree 1 and 2 over any finite field $\mathbb F_q$, and give out the explicit equations of del Pezzo surfaces that have unique rational point.
We completely classify K-stability of log del Pezzo hypersurfaces with index 2.
In this paper we consider del Pezzo surfaces with only log terminal singularities admitting an action of a finite simple group.
We investigate the characteristic numbers of Del Pezzo surfaces using degenerations.
We consider del Pezzo surfaces with du Val singularities. We'll prove that a del Pezzo surface $X$ with du Val singularities has a $-K_X$-polar cylinder if and only if there exist tiger such that the support of this tiger does not contain anti-canonical divisor. Also we classify all del Pezzo surfaces $X$ such that $X$ has not any cylinders.
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