Quartic double solids with ordinary singularities
M. I. Grooten, J. H. M. Steenbrink
本文研究了具有双二次曲线的四次曲面上的射影三维空间的双覆盖的三重分支的第三个同调群上的混合Hodge结构。我们处理的Torelli问题，这样的三倍。
We study the mixed Hodge structure on the third homology group of a threefold which is the double cover of projective three-space ramified over a quartic surface with a double conic. We deal with the Torelli problem for such threefolds.
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Deformation Classification of Quartic Surfaces with Simple Singularities
本文对作为 $K3$ 曲面的简单空间四次曲面进行了完整的等奇点形变分类。
On smooth surfaces in projective four-space lying on quartic hypersurfaces with isolated singularities
证明了射影四维空间中的一个非一般型的光滑曲面，如果它位于一个具有孤立奇点的四次超曲面上，它的度至多为27（实际上我们证明了一个稍微更一般的结果）。
We show, in this second part, that the maximal number of singular points of a quartic surface $X \subset \mathbb{P}^3_K$ defined over an algebraically closed field $K$ of characteristic 2 is at most 14, and that, if we have 14 singularities, these are nodes and moreover the minimal resolution of $X$ is a supersingular K3 surface. We produce an irreducible component, of dimension 24, of the variety of quartics with 14 nodes. We also exhibit easy examples of quartics with 7 $A_3$-singularities.
Singularities of normal quartic surfaces III (char=2, non-supersingular)
该研究针对特征2的代数闭域上的非超奇异正规四次曲面，证明其奇点最多12个，并给出适用于任意特征的显式例子族，推进了特征2下四次曲面奇点计数的相关研究。
We give a bound on the number of isolated, essential singularities of determinantal quartic surfaces in 3-space. We also provide examples of different configurations of real singularities on quartic surfaces with a definite Hermitian determinantal representation, and conjecture an extension of a theorem by Degtyarev and Itenberg.
On the ring of invariants of ordinary quartic curves in characteristic 2
本文计算了特征为2的普通四次曲线的一组完整的不变量。
We construct special conics configurations from some points configurations which are the singularities of the dual of a quartic curve.
We show, in this first part, that the maximal number of singular points of a normal quartic surface $X \subset \mathbb{P}^3_K$ defined over an algebraically closed field $K$ of characteristic $2$ is at most $16$. We produce examples with $14$, respectively $12$, singular points and show that, under several geometric assumptions ($\mathfrak S_4$-symmetry, or behaviour of the Gauss map, or structure of tangent cone at one of the singular points $P$, separability/inseparability of the projection with centre $P$), we can obtain smaller upper bounds for the number of singular points of $X$.
Q-factorial quartic threefolds
我们证明了一个节点四次三重$X$不包含任何平面是$Q$ -阶乘，只要它有不超过12个奇点，与一个四次正好有12个奇点包含一个二次曲面。我们给出了与后四次曲线有关的一些几何构造。
An ordinary plane of a finite set of points in real 3-space with no three collinear is a plane intersecting the set in exactly three points. We prove a structure theorem for sets of points spanning few ordinary planes. Our proof relies on Green and Tao's work on ordinary lines in the plane, combined with classical results on space quartic curves and non-generic projections of curves. This gives an alternative approach to Ball's recent results on ordinary planes, as well as extending them. We also give bounds on the number of coplanar quadruples determined by a finite set of points on a rationa…
On complete degenerations of surfaces with ordinary singularities in $\mathbb P^3$
本文研究了$\mathbb P^3$中具有普通奇点的曲面退化为一般位置的平面排列的存在性问题。
The log canonical thresholds of irreducible quasi-ordinary hypersurface singularities are computed, using an explicit list of pole candidates for the motivic zeta function found by the last two authors.
Ordinary $r$--tuples in cyclic quotient surface singularities
本文刻画了循环商曲面奇点中哪些Weil除子构成抽象的r-元组曲线奇点，揭示了奇点结构与除子性质之间的对应关系。
Bijectiveness of the Nash Map for Quasi-Ordinary Hypersurface Singularities
在本文中，我们给出了一个肯定的回答纳什关于弧空间的一个奇点，类的拟普通的超曲面奇点，在这种情况下，以前的结果和技术石井Shihoko。
In this paper we study some properties of the class of nu-quasi-ordinary hypersurface singularities. They are defined by a very mild condition on its (projected) Newton polygon. We associate with them a Newton tree and characterize quasi-ordinary hypersurface singularities among nu-quasi-ordinary hypersurface singularities in terms of their Newton tree. A formula to compute the discriminant of a quasi-ordinary Weierstrass polynomial in terms of the decorations of its Newton tree is given. This allows to compute the discriminant avoiding the use of determinants and even for non Weierstrass prep…
Toric embedded resolutions of quasi-ordinary hypersurface singularities
利用复解析超曲面的复环态射，建立了复解析超曲面的拟寻常奇点的两个嵌入式分解过程，其中复环态射只依赖于奇点的拟寻常投影的特征单项式.这个结果回答了Lipman在Equisingularity and simultaneous奇点的分解，奇点的分解，Progress in Mathematics No.181，2000，485-503中的一个公开问题。在第一个过程中，奇异性被嵌入为超曲面。在第二个过程中，这是灵感的工作戈尔丁和Teissier的平面曲线（见解决奇异的平面解析分支与一个环面态射，loc。引用，第315-340页），我们以一个环面态射提供其嵌入分辨率的方式将奇点重新嵌入到更大维度的仿射空间中。我们比较这两个程序，我们表明，他们符合适当的假设。
The geometric motivic Poincaré series of a germ $(S,0)$ of complex algebraic variety takes into account the classes in the Grothendieck ring of the jets of arcs through $(S,0)$. Denef and Loeser proved that this series has a rational form. We give an explicit description of this invariant when $(S,0)$ is an irreducible germ of quasi-ordinary hypersurface singularity in terms of the Newton polyhedra of the logarithmic jacobian ideals. These ideals are determined by the characteristic monomials of a quasi-ordinary branch parametrizing $(S,0)$.
Weak Ziegler pairs of conic-line arrangements with ordinary singularities
本文从弱 Ziegler 对视角研究平面上具拟齐次普通奇点的圆锥线排列，探讨复射影平面中曲线排列的自由性及 Numerical Terao's Conjecture，即排列的弱组合是否决定其自由性。
A quasi-ordinary polynomial is a monic polynomial with coefficients in the power series ring such that its discriminant equals a monomial up to unit. In this paper we study higher derivatives of quasi-ordinary polynomials, also called higher order polars. We find factorizations of these polars. Our research in this paper goes in two directions. We generalize the results of Casas-Alvero and our previous results on higher order polars in the plane to irreducible quasi-ordinary polynomials. We also generalize the factorization of the first polar of a quasi-ordinary polynomial (not necessary irred…
Two Magma functions are given: one computes linear systems of plane curves with non-ordinary singularities and the other computes a scheme which parametrizes given degree plane curves with given singularities. These functions provide an efficient tool to construct explicit equations of singular plane algebraic curves. By computing singular branch curves, we obtain equations of normal quartic surfaces in $\mathbb C\mathbb P^3$ having the following combinations of rational double points: $\mathsf D_5\mathsf E_7\mathsf E_7,$ $\mathsf D_7\mathsf D_6\mathsf D_6,$ $\mathsf E_6\mathsf D_8\mathsf D_5,…
Let $f(Y)\in K[[X_1,\dots,X_d]][Y]$ be a quasi-ordinary Weierstrass polynomial with coefficients in the ring of formal power series over an algebraically closed field of characteristic zero. In this paper we study the discriminant $D_f$ of $f(Y)-V$, where $V$ is a new variable. We show that the Newton polytope of $D_f$ depends only on contacts between the roots of $f(Y)$. Then we prove that $f(Y)$ is irreducible if and only if the Newton polytope of $D_f$ satisfies some arithmetic conditions. Finally we generalize these results to quasi-ordinary power series.
We study complex spatial quartic surfaces with simple singularities up to equisingular deformations; as a first step, give a complete equisingular deformation classification of the so-called non-special simple quartic surfaces.
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…
Birational rigidity of quartic three-folds with a double point of rank 3
本文证明复射影空间中仅含秩3二重点的一般四次三重流形具有双有理刚性，其双有理自映射群为25个2阶循环群的自由积，并由此推出刚性阶乘四次流形补集的余维数至少为3。
Derived categories of quartic double fivefolds
该研究通过扭曲的Calabi-Yau三重线构造了四次双五重线的导出范畴，并验证了Kuznetsov的有理性猜想和Reid的非交换幻想。
The Frobenius map, rank 2 vector bundles and Kummer's quartic surface in characteristic 2 and 3
设X是定义在特征p> 0的代数闭域k上亏格g> 1的光滑射影曲线。设M_X（r）是具有固定平凡行列式的半稳定秩r向量丛的模空间。相对Frobenius映射F：X \to X_1通过拉回导出有理映射V：M_{X_1}（r）\to M_X（r）。我们在以下两种情况下确定V的方程：（1）（g，r，p）=（2，2，2）和X非平凡且Hasse-Witt不变量等于1（对于X平凡的情况，参见数学AG/0005044），以及（2）（g，r，p）=（2，2，3）。我们还证明了，对于任何三元组（g，r，p），存在V的基点，即，半稳定丛E使得F ^* E不是半稳定的。
We present algorithms for reconstructing, up to unavoidable projective automorphisms, surfaces with ordinary singularities in three dimensional space starting from their silhouette, or "apparent contour" - namely the branching locus of a projection on the plane - and the projection of their singular locus.
Reduction of Plane Quartics and Dixmier-Ohno invariants
本文利用Dixmier-Ohno不变量刻画了平面四次曲线的奇点类型，并据此给出了判定亏格3非超椭圆曲线稳定约化类型的新准则。
We test the methods for computing the Picard group of a $K3$ surface in a situation of high rank. The examples chosen are resolutions of quartics in $\bP^3$ having 14 singularities of type $A_1$. Our computations show that the method of R. van Luijk works well when sufficiently large primes are used.
We consider the class of singular double coverings $X \to \PP^3$ ramified in the degeneration locus $D$ of a family of 2-dimensional quadrics. These are precisely the quartic double solids constructed by Artin and Mumford as examples of unirational but nonrational conic bundles. With such quartic surface $D$ one can associate an Enriques surface $S$ which is the factor of the blowup of $D$ by a natural involution acting without fixed points (such Enriques surfaces are known as nodal Enriques surfaces or Reye congruences). We show that the nontrivial part of the derived category of coherent she…
The Hodge spectrum is an important analytic invariant of singularities encoding the Hodge filtration and the monodromy of the Milnor fiber. Explicit formulas exist for only a few cases. In this article the main result is a combinatorial formula for homogeneous polynomials in three variables whose reduced one define projective curve arrangements having only ordinary multiple points.
Freeness of arrangements of lines and one conic with ordinary quasi-homogeneous singularities
本文研究由线和一个光滑圆锥组成的自由排列，通过弱组合学方法对具有准齐次普通奇点的排列进行不完全分类。
In this paper we give a complete description of the irreducible components of the jet schemes (with origin in the singular locus) of a two-dimensional quasi-ordinary hypersurface singularity. We associate with these components and with their codimensions and embedding dimensions, a weighted graph. We prove that the data of this weighted graph is equivalent to the data of the topological type of the singularity. We also determine a component of the jet schemes (or equivalently, a divisor on $\mathbb{A}^3$), that computes the log canonical threshold of the singularity embedded in $\mathbb{A}^3$.…
We describe the singularities and related properties of the arrangement of 21 reducible polars of Klein's quartic, containing Klein's well-known arrangement of $21$ lines.
We show that smooth curves in the same biliaison class on a hypersurface in $\mathbf{P}^3$ with ordinary singularities are linearly equivalent. We compute the invariants $h^0(\mathscr{I}_C(d))$, $h^1(\mathscr{I}_C(d))$ and $h^1(\mathscr{O}_C(d))$ of a curve $C$ on such a surface $X$ in terms of the cohomologies of divisors on the normalization of $X$. We then study general projections in $\mathbf{P}^3$ of curves lying on the rational normal scroll $S(a,b)\subset\mathbf{P}^{a+b+1}$. If we vary the curves in a linear system on $S(a,b)$ as well as the projections, we obtain a family of curves in …
As an application of universal polynomials for local and multi-singularities of maps, we revisit classical enumerative formulae of Salmon-Cayley-Zeuthen for projective surfaces and analogous formulae of Segre-(B.)Severi-Roth for projective $3$-folds. In particular, several examples of actual computation are given using universal polynomials for computing weighted Euler characteristics of singularity loci.
Quasi Ordinary Singularities, Essential Divisors and Poincare Series
本文通过单项赋值序列定义了拟超曲面奇点的Poincaré级数，证明其为有理函数及解析不变量，并证明其与特征单项式规范序列相互确定，从而刻画了奇点的嵌入拓扑类型。
Degenerations of elliptic quartics and K-moduli of Fano threefolds
本文研究经两次爆破构造的法诺三维簇的K-模空间，将其同构于带CM线丛线性化的VGIT商空间，分类了该形变族的K-(半/多)稳定成员，相关证明用到希尔伯特概型几何等新要素。
Birational rigidity and Q-factoriality of a singular double quadric
证明了光滑三维二次曲面在四次截面上分枝的结点Q-阶乘双覆盖$X$的双有理刚性，并计算了其双有理自同构群。我们还证明了$X$是Q-阶乘的，只要它至多有11个奇点;此外，我们给出了一个例子，这种类型的非Q-阶乘簇有12个简单的双重奇点。
Double spaces with isolated singularities
证明了在具有孤立奇点的次$2n$超曲面$F\subset\mathbb{P}^{n}$上的$\mathbb{P}^{n}$分支的双覆盖的非理性性，使得$n\ge 4$和超曲面$F$的每个奇点是普通的，即其切锥的投影是光滑的，其重数不超过$2(n-2)$ .
We investigate the existence of complete intersection threefolds $X \subset \mathbb{P}^n$ with only isolated, ordinary multiple points and we provide some sufficient conditions for their factoriality.
Given an irreducible hypersurface singularity of dimension $d$ (defined by a polynomial $f\in K[[ {\bf x} ]][z]$) and the projection to the affine space defined by $K[[ {\bf x} ]]$, we construct an invariant which detects whether the singularity is quasi-ordinary with respect to the projection. The construction uses a weighted version of Hironaka's characteristic polyhedron and successive embeddings of the singularity in affine spaces of higher dimensions. When $ f $ is quasi-ordinary, our invariant determines the semigroup of the singularity and hence it encodes the embedded topology of the s…
Defect of irreducible plane curves with simple singularities
本研究围绕Dimca提出的平面曲线亏量展开，推导了含结点、普通尖点与普通三重点的不可约平面曲线的亏量下界，证明高Arnold指数的约化简单奇异平面曲线不可能是自由曲线。
Klein's simple group $H$ of order $168$ is the automorphism group of the plane quartic curve $C$, called Klein quartic. By Torelli Theorem, the full automorphism group $G$ of the Jacobian $J=J(C)$ is the group of order $336$, obtained by adding minus identity to $H$. The quotient variety $J/G$ can be alternatively represented as the quotient $\mathbb C^3/\tilde G$ of the complex $3$-space by the complex crystallographic group $\tilde G$, the extension of $G$ by the period lattice of the Klein quartic. Moreover, it turns out that $\tilde G$ is generated by affine complex reflections. According …
On $\mathscr{M}$-arrangements of conics and lines with ordinary singularities
研究具有平凡奇点的二次曲线和直线的\(\mathscr{M}\)-排列，给出存在性数值约束，详细研究含一条二次曲线和直线的排列，构造新例子，证明实排列有界性，记录相关代数和模的正则性结果。
On Poincaré polynomials for plane curves with quasi-homogeneous singularities
本文定义组合庞加莱多项式，证明自由圆锥曲线-直线配置在普通拟齐次奇点下满足Terao型因式分解，并给出自由$d$-配置的组合约束。
In this paper we characterize the Blowing-up maps of ordinary singularities for which there exists a natural Gysin morphism, i.e. a bivariant class $θ\in Hom_{D(Y)}(Rπ_*\mathbb Q_X, \mathbb Q_Y)$, compatible with pullback and with restriction to the complement of the singularity.
On the divisor class group of double solids
对于在曲面$B\subset P_3(C)$上分枝的双实体$V\to P_3(C)$，我们给出了除子类群$Pic(\tilde{V}})$的一组生成元，它们是由$B$的结点上只有超孤立奇点的$B$的接触面表示的.作为应用，给出了$\tilde{V}$的积分上同调无2-挠的一个条件.如果$B$是一个四次曲面，则列出所有可能的情况。此外，我们还给出了$B$码的维数的一个新的下界.
We study nodal del Pezzo 3-folds of degree $1$ (also known as double Veronese cones) with $28$ singularities, which is the maximal possible number of singularities for such varieties. We show that they are in one-to-one correspondence with smooth plane quartics and use this correspondence to study their automorphism groups. As an application, we find all $G$-birationally rigid varieties of this kind, and construct an infinite number of non-conjugate embeddings of the group $\mathfrak{S}_4$ into the space Cremona group.
Analytical invariants of quasi-ordinary hypersurface singularities associated to divisorial valuations
研究了复奇异的解析不可约代数胚（X，0），通过考虑其解析代数的滤子及其相关的分次环，这些滤子由（X，0）的正规化（Y，0）的正规化爆破的例外因子的不可约分量的除数赋值所诱导，中心在Y的点0.若（X，0）是拟寻常超曲面奇点，则相应的分次环是复数域上的有限型代数，即半群所定义的非必然正规仿射复曲面簇的坐标环，它是（X，0）的解析不变量.这提供了（X，0）的归一化特征单项式的分析不变性的另一个证明。如果（X，0）是非必要正规环面簇的代数胚，我们用同样的方法证明了非必要正规环面簇的代数胚的同构问题的一个局部形式.
We construct a quartic threefold with L-rational singularities which has torsion in its middle homology group. This answers a question of Brown and Schnetz for all fields of characteristic zero.
We study the geometry of quintic threefolds $X\subset \mathbb{P}^4$ with only ordinary triple points as singularities. In particular, we show that if a quintic threefold $X$ has a reducible hyperplane section then $X$ has at most $10$ ordinary triple points, and that this bound is sharp. We construct various examples of quintic threefolds with triple points and discuss their defect.
We consider the derived category of an Artin-Mumford quartic double solid blown-up at ten ordinary double points. We show that it has a semi-orthogonal decomposition containing the derived category of the Enriques surface of a Reye congruence. This answers affirmatively a conjecture by Ingalls and Kuznetsov.
Let Y be a hypersurface in projective space having only ordinary double points as singularities. We prove a variant of a conjecture of L. Wotzlaw on an algebraic description of the graded quotients of the Hodge filtration on the top cohomology of the complement of Y except for certain degrees of the graded quotients, as well as its extension to the Milnor cohomology of a defining polynomial of Y for degrees a little bit lower than the middle. These partially generalize theorems of Griffiths and Steenbrink in the Y smooth case, and enable us to determine the structure of the pole order spectral…
We investigate the structure of a variety of new Moishezon twistor spaces, by utilizing the pluri-half-anti-canonical map from the twistor spaces. Each of these twistor spaces is bimeromorphic to a double covering of a scroll of planes over a rational normal curve, and the branch divisor of the double cover is a cut of the scroll by a quartic hypersurface. In particular, the double covering has a pencil of Del Pezzo surfaces of degree two. Correspondingly, the twistor spaces have a pencil of rational surfaces with big anti-canonical class. The base locus of the last pencil is a cycle of ration…
We study the deformation theory of a Q-Fano 3-fold with only terminal singularities. First, we show that the Kuranishi space of a Q-Fano 3-fold is smooth. Second, we show that every Q-Fano 3-fold with only "ordinary" terminal singularities is Q-smoothable, that is, it can be deformed to a Q-Fano 3-fold with only quotient singularities. Finally, we prove Q-smoothability of a Q-Fano 3-fold assuming the existence of a Du Val anticanonical element. As an application, we get the genus bound for primary Q-Fano 3-folds with Du Val anticanonical elements.
There exists a well established differential topological theory of singularities of ordinary differential equations. It has mainly studied scalar equations of low order. We propose an extension of the key concepts to arbitrary systems of ordinary or partial differential equations. Furthermore, we show how a combination of this geometric theory with (differential) algebraic tools allows us to make parts of the theory algorithmic. Our three main results are firstly a proof that even in the case of partial differential equations regular points are generic. Secondly, we present an algorithm for th…
The Einstein-Weyl spaces associated to Segre quartic surfaces
本研究找到亏格1的Segre四次曲面对应的紧致迷你扭量空间显式例子，其Einstein-Weyl空间的连通分支微分同胚于de Sitter空间，结构随Segre曲面形变并收敛到标准de Sitter结构，还借助曲面实节点构造了不可紧化的非紧复曲面例子。
A homotopical treatment of intersection cohomology recently developed by Chataur-Saralegui-Tanré associates a "perverse algebraic model" to every topological pseudomanifold, extending Sullivan's presentation of rational homotopy to intersection cohomology. In this context, there is a notion of "intersection-formality", measuring the vanishing of Massey products in intersection cohomology. In the present paper, we study the perverse algebraic model of complex projective varieties with isolated singularities. We endow such invariant with natural mixed Hodge structures. This allows us to prove so…
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