Klaus Altmann, Duco van Straten
We prove a vanishing theorem for the Hodge number h^21 of projective toric varieties provided by a certain class of polytopes. We explain how this Hodge number also gives information about the deformation theory of the toric Gorenstein singularity derived from the same polytope. In particular, the vanishing theorem for h^21 implies that these deformations are unobstructed.
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This paper studies the Hilbert scheme of a curve on a complete-intersection K-trivial threefold, in the case in which the curve is unobstructed in the ambient variety in which the threefold lives. The basic result is that the obstruction theory of the curve is completely determined by the scheme-theoretic Abel-Jacobi mapping. Several applications of this fact are given.
The class in the Brauer group of a quaternion algebra over a field is 2-torsion. We study the following question: Which 2-torsion elements of the Brauer group of a complex function field are representable by quaternion algebras? Using intersection theory to show that a certain cohomology class (on a smooth projective model) is the class of an algebraic cycle, we arrive at an obstruction, defined on a subgroup of the 2-torsion of the Brauer group, to representability by quaternion algebras. For the function fields of some complex threefolds, the obstruction map is computed and found to be nontr…
Given a smooth, projective variety $X$ and an effective divisor $D\,\subseteq\, X$, it is well-known that the (topological) obstruction to the deformation of the fundamental class of $D$ as a Hodge class, lies in $H^2(\mathcal{O}_X)$. In this article, we replace $H^2(\mathcal{O}_X)$ by $H^2_D(\mathcal{O}_X)$ and give an analogous topological obstruction theory. We compare the resulting local topological obstruction theory with the geometric obstruction theory (i.e., the obstruction to the deformation of $D$ as an effective Cartier divisor of a first order infinitesimal deformations of $X$). We…
In this paper we discuss an obstruction to the integral Hodge conjecture, which arises from certain behavior of vanishing cycles. This allows us to construct new counter-examples to the integral Hodge conjecture. One typical such counter-example is the product of a very general hypersurface of odd dimension and an Enriques surface. Our approach generalizes the degeneration argument of Benoist-Ottem.
Let $X$ be a compact complex manifold, consider a small deformation $ϕ: \mathcal{X} \to B$ of $X$, the dimension of the Dolbeault cohomology groups $H^q(X_t,Ω_{X_t}^p)$ may vary under this defromation. This paper will study such phenomenons by studying the obstructions to deform a class in $H^q(X,Ω_X^p)$ with the parameter $t$ and get the formula for the obstructions.
Twisted Hodge groups and deformation theory of Hilbert schemes of points on surfaces via Hodge modules
本研究利用Hodge模理论计算紧复曲面上点的Hilbert概形的扭曲Hodge数，证明了相关猜想修正版，推广了经典公式，并确定了Douady空间形变理论的切空间与障碍空间。
In this paper we prove that the cohomology of smooth projective tropical varieties verify the tropical analogs of three fundamental theorems which govern the cohomology of complex projective varieties: Hard Lefschetz theorem, Hodge-Riemann relations and monodromy-weight conjecture. On the way to establish these results, we introduce and prove other results of independent interest. This includes a generalization of the results of Adiprasito-Huh-Katz, Hodge theory for combinatorial geometries, to any unimodular quasi-projective fan having the same support as the Bergman fan of a matroid, a tropi…
On the deformation theory of Fourier-Mukai transforms between Calabi-Yau varieties
本文研究特征零与混合特征下全忠实 Fourier-Mukai 变换的形变理论，证明源簇具平凡典范丛时形变阻碍可由 Hodge 理论完全控制，推广已有结果并给出阻碍类的上积公式。
We define the Z/2Z Hodge spaces H_{pq}(Σ) of a fan Σ. If Σis the normal fan of a reflexive polytope Δthen we use polyhedral duality to compute the Z/2Z Hodge Spaces of Σ. In particular, if the cones of dimension at most e in the face fan Σ^* of Δare smooth then we compute H_{pq}(Σ) for p<e-1. If Σ^* is a smooth fan then we completely determine the spaces H_{pq}(Σ) and we show the toric variety X associated to Σis maximal, meaning that the sum of the Z/2Z Betti numbers of X(R) is equal to the sum of the Z/2Z Betti numbers of X(C).
We give an algorithm that takes a smooth hypersurface over a number field and computes a $p$-adic approximation of the obstruction map on the Tate classes of a finite reduction. This gives an upper bound on the "middle Picard number" of the hypersurface. The improvement over existing methods is that our method relies only on a single prime reduction and gives the possibility of cutting down on the dimension of Tate classes by two or more. The obstruction map comes from $p$-adic variational Hodge conjecture and we rely on the recent advancement by Bloch-Esnault-Kerz to interpret our bounds.
Local cohomology and singular cohomology of toric varieties via mixed Hodge modules
本文利用混合 Hodge 模块技术研究了环面簇的局部上同调与奇异上同调，证明了真环面簇奇异上同调的混合 Hodge-Tate 型性质，并详细计算了特定子类的局部上同调与 Betti 数。
Infinitesimal invariants of mixed Hodge structures II: Log Clemens conjecture and log connectivity
本文研究混合Hodge结构的无穷小不变量，提出Log克莱门斯猜想并建立非消失性判据，推广了Calabi-Yau情形的对称性。
The motivic nearby fiber is an invariant obtained from degenerating a complex variety over a disc. It specializes to the Euler characteristic of the original variety but also contains information on the variation of Hodge structure associated to the degeneration which is encoded as a limit mixed Hodge structure. However, this invariant is difficult to compute in practice. Using the techniques of tropical geometry we present a new formula for the motivic nearby fiber. Moreover, since there is a range of available software implementing the main algorithms in tropical geometry, our formula can be…
From Regions to Hodge Structures: The Topological Study of semialgebraic Curves Configurations
研究半代数曲线配置的拓扑，通过局部节点贡献ψ发展组合理论，证明区域计数公式等，在代数设置中研究相关条件及差异，引入二项式节点不变量，揭示精确性障碍与关联数据关系及\(\psi\)与不变量关系。
Semiregularity as a consequence of Goodwillie's theorem
本文通过将半正则映射实现为导出模叠上广义Abel-Jacobi映射的切映射，利用Goodwillie定理证明半正则性猜想，并推广至奇异簇与导出叠，为约化不变量理论提供障碍理论。
Diffeological non-Abelian Hodge theory: relative harmonic metrics and deformation theory
研究紧致凯勒流形\(X\)上希格斯丛和平坦丛的微分几何模栈，通过构建相对解析理论，证明稳定希格斯族存在全局光滑调和度量，刻画扩张生成栈，分析热流数据损失并构造光滑霍奇\(\lambda\)族。
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