Davide Frapporti, Kyoung-Seog Lee
In this paper, we study effective, nef and semiample cones of surfaces isogenous to a product of mixed type with $p_g=0$. In particular, we prove that all reducible fake quadrics are Mori dream surfaces.
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On the minimal model of semi-isogenous mixed surfaces
本文确定了具有χ=1和K^2>0的半等基因混合曲面的极小模型，通过推广轨道除子方法构造有效除子，解决了该曲面的极小模型问题。
Let $C$ be a smooth projective curve and $G$ a finite subgroup of $\mathrm{Aut}(C)^2\rtimes \mathbb Z_2$ whose action is \textit{mixed}, i.e.~there are elements in $G$ exchanging the two isotrivial fibrations of $C\times C$. Let $G^0\triangleleft G$ be the index two subgroup $G\cap\mathrm{Aut}(C)^2$. If $G^0$ acts freely, then $X:=(C\times C)/G$ is smooth and we call it \textit{semi-isogenous mixed surface}. In this paper we give an algorithm to determine semi-isogenous mixed surfaces with given geometric genus, irregularity and self-intersection of the canonical class. As an application we cl…
In this paper we study \emph{threefolds isogenous to a product of mixed type} i.e. quotients of a product of three compact Riemann surfaces $C_i$ of genus at least two by the action of a finite group $G$, which is free, but not diagonal. In particular, we are interested in the systematic construction and classification of these varieties. Our main result is the full classification of threefolds isogenous to a product of mixed type with $χ(\mathcal O_X)=-1$ assuming that any automorphism in $G$, which restricts to the trivial element in $Aut(C_i)$ for some $C_i$, is the identity on the product.…
We recall that a smooth ample surface $\mathcal{S}$ in a general $(1,2,2)$-polarized abelian threefold, which is the pullback of the Theta divisor of a smooth plane quartic curve $\mathcal{D}$, is a surface isogenous to the product $\mathcal{C} \times \mathcal{C}$, where $\mathcal{C}$ is a genus $9$ curve embedded in $\mathbb{P}^3$ as complete intersection of a smooth quadric and a smooth quartic. We show that the space of global holomorhic sections of the canonical bundle of this surface is generated by certain determinantal bihomogeneous polynomials of bidegree $(2,2)$ on $\mathbb{P}^3$, whi…
Mixed Hodge Structures on Generalized Theta Divisors and Graph Motives
本文研究一般化θ除子上的混合Hodge结构，并探讨其与图动机的可能联系。
We use filtered log-$\mathscr{D}$-modules to represent the (dual) localization of Saito's Mixed Hodge Modules along a smooth hypersurface, and show that they also behave well under the direct image functor and the dual functor in the derived category of filtered log-$\mathscr{D}$-modules. The results of this paper can be used to generalize the result of M. Popa and C. Schnell about Kodaira dimension and zeros of holomorphic one-forms into the log setting.
Let K(X) be the collection of all non-zero finite dimensional subspaces of rational functions on an n-dimensional irreducible variety X. For any n-tuple L_1,..., L_n in K(X), we define an intersection index [L_1,..., L_n] as the number of solutions in X of a system of equations f_1 = ... = f_n = 0 where each f_i is a generic function from the space L_i. In counting the solutions, we neglect the solutions x at which all the functions in some space L_i vanish as well as the solutions at which at least one function from some subspace L_i has a pole. The collection K(X) is a commutative semigroup …
Mixed mock modularity of special divisors
本文证明了正交Shimura簇环面紧化中特殊除数的生成级数是混合mock模形式，并通过锥分解中射线相关的theta级数给出显式完备化，证明依赖于边界相交理论。
Cyclic covers via mixed Hodge modules
本文针对复代数簇上由线丛整体截面定义的有效卡蒂埃除子，用混合霍奇模理论描述其N重循环覆盖的构造方法。
We study mixed surfaces, the minimal resolution S of the singularities of a quotient (C x C)/G of the "square" of a curve by a finite group G of automorphisms that contains elements not preserving the factors. We study them through the "further quotients" by (C x C)/G' where G' contains G. As a first application we prove that if the irregularity is at least 3, then S is also minimal. The result is sharp. The main result is a complete description of the Albanese morphism of S through a determined further quotient (C x C)/G' that is an étale cover of the symmetric square of a curve. In particula…
We introduce toric $b$-divisors on complete smooth toric varieties and a notion of integrability of such divisors. We show that under some positivity assumptions toric $b$-divisors are integrable and that their degree is given as the volume of a convex set. Moreover, we show that the dimension of the space of global sections of a nef toric $b$-divisor is equal to the number of lattice points in this convex set and we give a Hilbert--Samuel type formula for its asymptotic growth. This generalizes classical results for classical toric divisors on toric varieties. Finally, we relate convex bodies…
On the geometry of the Humbert surface of square discriminant
该研究确定了平方判别式Humbert曲面的Enriques--Kodaira型，通过构造对角Hirzebruch--Zagier除子分析Fricke型对合不动点，得到含扩张Cartan子群模曲线情形的亏格公式。
Normal hyperplane sections of normal schemes in mixed characteristic
本文研究了混合特征下正常方案的正常超平面截面，证明了在一定条件下存在无限多个正常有效Cartier除子，并应用该结果证明了除子类群限制映射的Grothendieck-Lefschetz类型结果。
Correspondences between convex geometry and complex geometry
本文建立凸几何与复几何（全纯线丛理论）的类比，研究正乘积与混合体积的关系，定义除子类的布拉施克加法并证明新不等式，同时将亚历山德罗夫体构造和闵可夫斯基存在定理分别对应为除子扎里斯基分解和锥对偶性的凸几何版本。
We compute the cones of effective divisors on blowups of $\mathbb{P}^1 \times \mathbb{P}^2$ and $\mathbb{P}^1 \times \mathbb{P}^3$ in up to 6 points. We also show that all these varieties are log Fano, giving a conceptual explanation for the fact that all the cones we compute are rational polyhedral.
Given a compact Riemann surface $\bar{X}$ of genus $g$ and a point $q$ on $\bar{X}$, we consider $X:=\bar{X}\setminus\{q\}$ with a basepoint $p\in X$. The extension of mixed Hodge structures, given by the weights -1 and -2, of the mixed Hodge structure on the fundamental group (in the sense of Hain) is studied. We show that it naturally corresponds on the one hand to the element $(2g q-2 p-K)$ in $\Pic^0(\bar{X})$, where $K$ represents the canonical divisor, and on the other hand to the respective extension of $\bar{X}$. Finally, we prove a pointed Torelli theorem for punctured Riemann surface…
We first recall the construction of the Chow motive modelling intersection cohomology of a proper surface and study its fundamental properties. Using Voevodsky's category of effective geometrical motives, we then study the motive of the exceptional divisor in a non-singular blow-up. If all geometric irreducible components of the divisor are of genus zero, then Voevodsky's formalism allows us to construct certain one-extensions of Chow motives, as canonical sub-quotients of the motive with compact support of the smooth part of the surface. Specializing to Hilbert--Blumenthal surfaces, we recove…
Non-nef loci in mixed characteristic
本文引入非丰轨迹与限制基轨迹的相对版本，证明特征零戴德金环上适度奇点射影平坦正规整概型的对应Boucksom--Broustet--Pacienza猜想成立，是相关特征结果的混合特征类似物。
For a cycle of codimension 1 in a toric variety, its degree with respect to a nef toric divisor can be understood in terms of the mixed volume of the polytopes associated to the divisor and to the cycle. We prove here that an analogous combinatorial formula holds in the arithmetic setting: the global height of a 1-codimensional cycle with respect to a toric divisor equipped with a semipositive toric metric can be expressed in terms of mixed integrals of the $v$-adic roof functions associated to the metric and the Legendre-Fenchel dual of the $v$-adic Ronkin function of the Laurent polynomial o…
Let $\V$ be a mixed characteristic complete discrete valuation ring, let $\X$ and $\Y$ be two smooth formal $\V$-schemes, let $f_0$ : $X \to Y$ be a projective morphism between their special fibers, let $T$ be a divisor of $Y$ such that $T_X := f_0 ^{-1} (T) $ is a divisor of $X$ and let $\M \in D ^\mathrm{b}_\mathrm{coh} (\D ^†_{\X} (\hdag T_X)_{\Q})$. We construct the relative duality isomorphism $ f_{0T +} \circ \DD_{\X, T_X} (\M) \riso \DD_{\Y, T} \circ f_{0T +} (\M)$. This generalizes the known case when there exists a lifting $f : \X \to \Y$ of $f_{0}$. Moreover, when $f_0$ is a closed i…
Let $S_{0}, S_{1}$ and $S_{2}$ be connected Riemann surfaces and let $β_{1}:S_{1} \to S_{0}$ and $β_{2}:S_{2} \to S_{0}$ be surjective holomorphic maps. The associated fiber product $S_{1} \times_{(β_{1},β_{2})} S_{2}$ has the structure of a singular Riemann surface, endowed with a canonical map $β$ to $S_{0}$ satisfying that $β_{j} \circ π_{j}=β$, where $π_{j}$ is coordinate projection onto $S_{j}$. In this paper we provide a Fuchsian description of the fiber product and obtain that if one the maps $β_{j}$ is a regular branched cover, then all its irreducible components are isomorphic. In the…
Graphs of Hecke operators in mixed ramification
本文研究了在分歧$G$-束模空间上Hecke算子，引入了$\mathcal H$-分歧概念，证明在弱正则条件下，深cusp处的Hecke算子作用在复杂分歧时类似于简单分歧，从而减少研究案例数量。
Lifting negative curves from finite fields and Seshadri constants at ten points
本文通过有限域计算与混合特征形变，在十个一般点处构造 nef 除子，将 Seshadri 常数下界改进至 8658/27379。
The main problem addressed in the paper is the Torelli problem for n-dimensional varieties of general type, more specifically for varieties with ample canonical bundle. It asks under which geometrical condition for a variety the period map for the Hodge structure of weight n is a local embedding. We define a line bundle to be almost very ample iff the associated linear system is base point free and yields an injective morphism. We define instead a line bundle to be quasi very ample if it yields a birational morphism which is a local embedding on the complement of a finite set. Our main result …
We study a K3 surface, which appears in the two-loop mixed electroweak-quantum chromodynamic virtual corrections to Drell--Yan scattering. A detailed analysis of the geometric Picard lattice is presented, computing its rank and discriminant in two independent ways: first using explicit divisors on the surface and then using an explicit elliptic fibration. We also study in detail the elliptic fibrations of the surface and use them to provide an explicit Shioda--Inose structure. Moreover, we point out the physical relevance of our results.
Rational Homotopy Type of Complements of Submanifold Arrangements
本文通过构造cdga模型，研究了子流形排列补集的有理同调类型，并推广了多个关于排列补集的已知结果。
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