Suppose that Y is a cyclic cover of projective space branched over a hyperplane arrangement D, and that U is the complement of the ramification locus in Y. The first theorem implies that the Beilinson-Hodge conjecture holds for U if certain multiplicities of D are coprime to the degree of the cover. For instance this applies when D is reduced with normal crossings. The second theorem shows that when D has normal crossings and the degree of the cover is a prime number, the generalized Hodge conjecture holds for any toroidal resolution of Y. The last section contains some partial extensions to more general nonabelian covers.
For two varieties of dimension $5$ constructed as double covers of ${\mathbb P}^5$ branched along the union of $12$ hyperplanes, we prove that the number of points over ${\mathbb F}_p$ can be expressed in terms of Artin symbols and the $p$th Fourier coefficients of modular forms. Many analogous results are known in dimension $\le 3$, but very few in higher dimension. In addition, we use an idea of Burek to construct quotients of our varieties for which the point counts mod $p$ are expressible in terms of Artin symbols and the coefficients of a single modular form of weight $6$.
For each complex central essential hyperplane arrangement $\mathcal{A}$, let $F_{\mathcal{A}}$ denote its Milnor fiber. We use Tevelev's theory of tropical compactifications to study invariants related to the mixed Hodge structure on the cohomology of $F_{\mathcal{A}}$. We prove that the map taking each arrangement $\mathcal{A}$ to the Hodge-Deligne polynomial of $F_{\mathcal{A}}$ is locally constant on the realization space of any loop-free matroid. When $\mathcal{A}$ consists of distinct hyperplanes, we also give a combinatorial description for the homotopy type of the boundary complex of an…
Given a reduced effective divisor D on a smooth variety X, we describe the generating function for the classes of the Hodge ideals of D in the Grothendieck group of coherent sheaves on X in terms of the motivic Chern class of the complement of the support of D. As an application, we compute the generating function for the Hilbert series of Hodge ideals of a hyperplane arrangement in terms of the Poincare polynomial of the arrangement.
Geometric monodromy of double covers of $\mathbb{P}^n$ branched along hyperplane arrangements
Beijing Institute of Mathematical Sciences and Applications（北京数学与应用科学研究所）；School of Mathematical Sciences, University of Science and Technology of China（中国科学技术大学数学科学学院）
A-D-E diagrams, Hodge--Tate hyperplane sections and semisimple quantum cohomology
PUC-Rio（天主教里约热内卢大学）；The Institute of Mathematical Sciences and Department of Mathematics, The Chinese University of Hong Kong（香港中文大学数学科学研究所及数学系）；School of Mathematics, Sun Yat-sen University（中山大学数学学院）；Department of Mathematics, University of Michigan（密歇根大学数学系）
Let $Y$ be a projective submanifold of the total space of the inverse of a very ample line bundle $π:L^{-1}\rightarrow B$ over a projective manifold $B$. Any section of $L^{-1}\rightarrow B$ is isomorphic to $B$ and the Hodge numbers of any proper smooth multisection are determined by the degree $d$ of that multi-section as are the Hodge numbers of any smooth complete intersection of multi-sections of degrees $\left(d_{1},\ldots,d_{r}\right)$. In this paper recursive formulae are given for those Hodge numbers in terms of the integers $\left\{ d_{1},\ldots,d_{r}\right\} $ and the Hodge numbers …
We study the moduli space of pairs $(X,H)$ consisting of a cubic threefold $X$ and a hyperplane $H$ in $\mathbb P^4$. The interest in this moduli comes from two sources: the study of certain weighted hypersurfaces whose middle cohomology admit Hodge structures of $K3$ type and, on the other hand, the study of the singularity $O_{16}$ (the cone over a cubic surface). In this paper, we give a Hodge theoretic construction of the moduli space of cubic pairs by relating $(X,H)$ to certain "lattice polarized" cubic fourfolds $Y$. A period map for the pairs $(X,H)$ is then defined using the periods o…
We prove a conjecture of Teissier asserting that if $f$ has an isolated singularity at $P$ and $H$ is a smooth hypersurface through $P$, then $\widetildeα_P(f)\geq \widetildeα_P(f\vert_H)+\frac{1}{θ_P(f)+1}$, where $\widetildeα_P(f)$ and $\widetildeα_P(f\vert_H)$ are the minimal exponents at $P$ of $f$ and $f\vert_H$, respectively, and $θ_P(f)$ is an invariant obtained by comparing the integral closures of the powers of the Jacobian ideal of $f$ and of the ideal defining $P$. The proof builds on the approaches of Loeser and Elduque-Mustata. The new ingredients are a result concerning the behav…
Let $f\colon S'\longrightarrow S$ be a cyclic branched covering of smooth projective surfaces over $\mathbb{C}$ whose branch locus $Δ\subset S$ is a smooth ample divisor. Pick a very ample complete linear system $|\mathcal{H}|$ on $S$, such that the polarized surface $(S, |\mathcal{H}|)$ is not a scroll nor has rational hyperplane sections. For the general member $[C]\in|\mathcal{H}|$ consider the $μ_{n}$-equivariant isogeny decomposition of the Prym variety $Prym(C'/C)$ of the induced covering $f\colon C'= f^{-1}(C)\longrightarrow C$:\[Prym(C'/C)\sim\prod_{d|n,\ d\neq1}\mathcal{P}_{d}(C'/C).\…
In this paper, we prove the irreducibility of the monodromy action on the anti-invariant part of the vanishing cohomology on a double cover of a very general element in an ample hypersurface of a complex smooth projective variety branched at an ample divisor. As an application, we study dominant rational maps from a double cover of a very general surface $S$ of degree$\geq 7$ in ${\mathbb P}^3$ branched at a very general quadric surface to smooth projective surfaces $Z$. Our method combines the classification theory of algebraic surfaces, deformation theory, and Hodge theory.
Given a very ample line bundle on a smooth projective variety, the variation of Hodge structure associated to the universal family of hyperplane sections can be thought of as a $D$-module with action generated by the Gauss-Manin connection. The decomposition theorem for a projective morphism and results similar to the Lefschetz hyperplane theorem tell us that the only nontrivial part of this VHS occurs in the middle degree corresponding to the vanishing cohomology of the hyperplane sections. We use Nori's connectivity theorem to give an explicit description of the cohomology sheaves of the de …
Vector bundles on curves coming from Variation of Hodge Structures
曲线上Kähler纤维空间的藤田第二定理断言相对对偶层的直像$V$分裂为直和$ V = A \oplus Q$，其中$A$是充分的，$Q$是酉平坦的。我们专注于我们的否定答案（\cite{cd}）藤田的问题：$V$是半样本？我们在这里给一个无限系列的反例使用超几何积分，我们给一个简单的参数，以表明monodromy表示是无限的。我们的反例是表面的一般类型的正指数，明确给出阿贝尔覆盖与组$(\mathbb Z/n)^2$的Del Pezzo表面的程度为5（分支上的工会线形成一个bianticanonical因子），并赋予一个半稳定的纤维化只有$3$奇异纤维。最简单的这类曲面是三球曲面，在I. Bauer和第一作者，在$2$属的曲线上，以及在$4$属的纤维上进行了交叉。这些例子是一个更大的类比相应的志村曲线在模空间的阿贝尔品种。
