Mondromy and deformation-and-specialization arguments are used to produce a pencil of Enriques surfaces with no section and index one. The same technique completes the proof that the witness curves in "Rational connectivity ..." depend on the relative dimension.
The three pencils of K3 surfaces of minimal discriminant whose general element covers at least one Enriques surface are Kondō's pencils I and II, and the Apéry--Fermi pencil. We enumerate and investigate all Enriques surfaces covered by their general elements.
We prove that there exists a pencil of Enriques surfaces defined over $\mathbb{Q}$ with non-algebraic integral Hodge classes of non-torsion type. This gives the first example of a threefold with the trivial Chow group of zero-cycles on which the integral Hodge conjecture fails. As an application, we construct a fourfold which gives the negative answer to a classical question of Murre on the universality of the Abel-Jacobi maps in codimension three.
Let $X$ be a smooth projective K3 surface over complex numbers and $C$ be an ample curve on $X$. In this paper we will study the semistability of the Lazarsfeld-Mukai bundle $E_{C, A}$ associated to a line bundle $A$ ion $C$ such that $|A|$ is a pencil on $C$ and computes the Clifford index of $C$. We give a necessary and sufficient condition for $E_{C, A}$ being semistable.
In this note, we prove that the syzygy bundle $M_L$ is cohomologically stable with respect to $L$ for any ample and globally generated line bundle $L$ on an Enriques (resp. bielliptic) surface over an algebraically closed field of characteristic $\neq 2$ (resp. $\neq 2,3$). In particular our result on complex Enriques surfaces improves a result of Torres-López and Zamora by removing a condition on Clifford index. Together with the results of Camere and Caucci--Lahoz, it implies that $M_L$ is stable with respect to $L$ for an ample and globally generated line bundle $L$ on any smooth minimal co…
Mori dream surfaces associated with curves with one place at infinity
我们研究了一类有理曲面(在[Campillo,Piltant和Reguera,2005]中考虑)与曲线在无穷远处有一个地方,并明确描述了这些曲面上的Cox环和线丛的整体瓣的生成元。特别地,我们证明了它们的Cox环是双生成的,即它们是Mori梦空间。我们还计算了它们的“无穷大处的全局Zeroki半群”(由“无穷大处"没有基点的线丛组成)和“全局Enriques半群”(由C^2中曲线的闭包生成)。特别地,我们证明了无穷远处的整体Zapriki半群和无穷远处等奇异的锥对应的曲面的Enriques半群是同构的,从而回答了[Campillo,Piltant and Reguera-Lopez,2002]的一个问题.我们还给出了一个有效的算法,以确定是否(理性)表面“承认系统的数值curvettes”(这些表面也被认为是在[Campillo,Piltant和Reguera,2005])。
We introduce a holomorphic torsion invariant of log-Enriques surfaces of index two with cyclic quotient singularities of type $\frac{1}{4}(1,1)$. The moduli space of such log-Enriques surfaces with $k$ singular points is a modular variety of orthogonal type %of dimension $10-k$ associated with a unimodular lattice of signature $(2,10-k)$. We prove that the invariant, viewed as a function on the modular variety, is given by the Petersson norm of an explicit Borcherds product. We note that this torsion invariant is essentially the BCOV invariant in the complex dimension $2$. As a consequence, th…
设X是具有对合g的K3曲面,该对合g具有非空固定轨迹X^g并且非平凡地作用在非零全纯2-形式上。我们将从指数至多为2的log del Pezzo曲面或有理椭圆曲面的一些更好的双覆盖中,以规范的方式构造所有这样的对(X,g),并构造X^g包含10(最大可能)条曲线的三种极值情形中的每一种的唯一族。我们还分类合理的日志Enriques表面的指数为2。我们的方法更多的是几何的,而不是晶格理论的(见Nikulin的论文,后者的方法)。