Nicolas Addington, Brendan Hassett, Yuri Tschinkel, Anthony Várilly-Alvarado
We exhibit new examples of rational cubic fourfolds, parametrized by a countably infinite union of codimension-two subvarieties in the moduli space. Our examples are fibered in sextic del Pezzo surfaces over the projective plane; they are rational whenever the fibration has a rational section.
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We study sextic del Pezzo surface fibrations via root stacks.
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.
In this paper, we study a sextic del Pezzo fibration over a curve comprehensively. We obtain certain formulae of several basic invariants of such a fibration. We also establish the embedding theorem of such a fibration which asserts that every such a fibration is a relative linear section of a Mori fiber space with the general fiber $(\mathbb{P}^{1})^{3}$ and that with the general fiber $(\mathbb{P}^{2})^{2}$. As an application of this embedding theorem, we classify singular fibers of such a fibrations and answer a question of T. Fujita about existence of non-normal fibers.
We construct a natural semiorthogonal decomposition for the derived category of an arbitrary flat family of sextic del Pezzo surfaces with at worst du Val singularities. This decomposition has three components equivalent to twisted derived categories of finite flat schemes of degrees 1, 3, and 2 over the base of the family. We provide a modular interpretation for these schemes and compute them explicitly in a number of standard families. For two such families the computation is based on a symmetric version of homological projective duality for $\mathbb{P}^2 \times \mathbb{P}^2$ and $\mathbb{P}…
Birational Geometry of sextic del Pezzo surfaces
该研究针对任意完美域上皮卡数为1的6次del Pezzo曲面，运用Galois上同调技术完成双正则分类与自同构群计算，解答了相关公开问题，证明其为唯一具无限柔韧性的立体曲面，并构造了双有理变换群的非平凡商。
Real-fibered morphisms of del Pezzo surfaces and conic bundles
本文基于 Ahlfors 关于实曲线的结果，利用拓扑环绕数刻画高维实代数簇的实纤维线性投影，并完整分类实 del Pezzo 曲面到射影平面的相关态射，同时探讨实圆锥丛。
Let Q -> B be a quadric fibration and T -> B a family of sextic du Val del Pezzo surfaces. Making use of the recent theory of noncommutative mixed motives, we establish a precise relation between the Schur-finiteness conjecture for Q, resp. for T, and the Schur-finiteness conjecture for B. As an application, we prove the Schur-finiteness conjecture for Q, resp. for T, when B is low-dimensional. Along the way, we obtain a proof of the Schur-finiteness conjecture for smooth complete intersections of two or three quadric hypersurfaces. Finally, we prove similar results for the Bass-finiteness con…
The intersection of a quadric and a cubic surface in 3-space is a canonical curve of genus 4. It has 120 complex tritangent planes. We present algorithms for computing real tritangents, and we study the associated discriminants. We focus on space sextics that arise from del Pezzo surfaces of degree one. Their numbers of planes that are tangent at three real points vary widely; both 0 and 120 are attained. This solves a problem suggested by Arnold Emch in 1928.
Given a degree one del Pezzo surface with canonical singularities, the linear series generated by twice the anti-canonical divisor exhibits the surface as the double cover of the quadric cone branched along a sextic curve. It is natural to ask if this description extends to the boundary of a compactification of the moduli space of degree one del Pezzo surfaces. The goal of this paper is to show that this is indeed the case. In particular, we give an explicit classification of the boundary of the moduli space of anti-canonically polarized broken del Pezzo surfaces of degree one as double covers…
Moduli of Nodal Sextic Curves via Periods of K3 Surfaces
本文研究了节点六次曲线的模空间，通过将其实现为IV型算术商的开放子空间，证明了GIT紧化与Looijenga紧化之间的同构，并将结果推广至具有特定对称性的情形。
We construct two small resolutions of singularities of the Coble fourfold (the double cover of the four-dimensional projective space branched over the Igusa quartic). We use them to show that all $S_6$-invariant three-dimensional quartics are birational to conic bundles over the quintic del Pezzo surface with the discriminant curves from the Wiman-Edge pencil. As an application, we check that $S_6$-invariant three-dimensional quartics are unirational, obtain new proofs of rationality of four special quartics among them and irrationality of the others, and describe their Weil divisor class grou…
Varieties fibered into del Pezzo surfaces form a class of possible outputs of the minimal model program. It is known that del Pezzo fibrations of degrees $1$ and $2$ over the projective line with smooth total space satisfying the so-called $K^2$-condition are birationally rigid: their Mori fibre space structure is unique. This implies that they are not birational to any Fano varieties, conic bundles or other del Pezzo fibrations. In particular, they are irrational. The families of del Pezzo fibrations with smooth total space of degree $2$ are rather special, as for "most" families a general de…
We provide a semiorthogonal decomposition for the derived category of fibrations of quintic del Pezzo surfaces with rational Gorenstein singularities. There are three components, two of which are equivalent to the derived categories of the base and the remaining non-trivial component is equivalent to the derived category of a flat and finite of degree 5 scheme over the base. We introduce two methods for the construction of the decomposition. One is the moduli space approach following the work of Kuznetsov on the sextic del Pezzo fibrations and the components are given by the derived categories…
Rational fibered cubic fourfolds
该研究在三次四折体模空间中探究多类已知有理三次除子的交，刻画其不可约分支，给出新的有理del Pezzo曲面或二次曲面纤维化三次四折体显式例子，并研究纤维化有理截面与Brauer类的对应关系。
We explain a classical construction of a del Pezzo surface of degree d = 4 or 5 as a smooth order two congruence of lines in 3-space whose focal surface is a quartic surface $X_{20-d}$ with 20-d ordinary double points. We also show that $X_{15}$ can be realized as a hyperplane section of the Castelnuovo-Richmond-Igusa quartic hypersurface. This leads to the proof of rationality of the moduli space of 15-nodal quartic surfaces. We discuss some other birational models of $X_{15}$: quartic symmetroids, 5-nodal quartic surfaces, 10-nodal sextic surfaces in $P^4$ and nonsingular surfaces of degree …
Cubic fourfolds containing a plane and a quintic del Pezzo surface
我们孤立出一类光滑有理三次四重曲面X，X包含一个平面，其相关的二次曲面丛不具有有理截面。这等价于由X产生的2次K3曲面S上偶Clifford代数的Brauer类的非平凡性。具体地说，我们证明了在三次四重数的模空间中，因子C_8和C_14的交有五个不可约分量。在对应于二次丛的六次退化曲线的切二次曲线的存在性的分支中，我们证明了一般成员既是pf函数又具有非平凡的Brauer类。这样的三次四重也提供了2次和14次K3曲面之间的扭曲导出等价，因此进一步证实了库兹涅佐夫关于三次四重的合理性的导出范畴猜想。
Classification of sextic curves in the Fano 3-fold $\mathcal{V}_5$ with rational Galois covers in ${\mathbb P}^3$
本文对法诺三维簇 $\bf \text{ℱ}_5$ 中具有复射影空间 ${\bf \text{ℙ}}^3$ 有理伽罗瓦覆盖的六次曲线分类，证明其模空间为复二维，并提出通过伽罗瓦覆盖理解该模空间的问题。
We determine several classes of smooth complex projective surfaces on which Zariski decomposition can be combined with vanishing theorems to yield cohomology formulae for all line bundles. The obtained formulae express cohomologies in terms of divisor class intersections, and are adapted to the decomposition of the effective cone into Zariski chambers. In particular, we show this occurs on generalised del Pezzo surfaces, toric surfaces, and K3 surfaces. In the second part we use these surface results to derive formulae for all line bundle cohomology on a simple class of elliptically fibered Ca…
Classification of log del Pezzo surfaces of index $\le 2$
这是我们工作的扩展版本[AN88]，1988年，俄语。我们分类的del Pezzo曲面在C上的日志终端奇异指数\le 2。通过分类，我们理解了所有例外曲线在奇点的适当（比最小的略强）奇点的分解上的交图的描述，以及收缩到奇点的曲线的子图。最后的结果是类似于经典的结果分类的非奇异del Pezzo曲面和使用通常的有限根系。然而，中间的考虑使用K3曲面的理论（特别是具有非辛对合的K3曲面）和双曲空间中的反射群的理论（特别是双曲格的反射群）。作为一个“基本”应用，我们的结果允许我们对P^2中具有简单奇点和几何亏格\ge 2的一个分支的六次曲线进行分类。
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