Meirav Amram, Mina Teicher
This paper is the second in a series of three papers concerning the surface T times T, where T is a complex torus. We compute the fundamental group of the branch curve of the surface in C^2, using the van Kampen Theorem and the braid monodromy factorization of the curve.
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Non-cycle triple planes with branch curve of degree at most 10
本文研究了分支曲线次数不超过10的正常非循环三重覆盖的分类问题。
A well-known and difficult problem in computational number theory and algebraic geometry is to write down equations for branched covers of algebraic curves with specified monodromy type. In this article, we present a technique for computing such covers in the case of totally ramified covers of elliptic curves branched at one point.
In this paper we prove that the branch curve of a general projection of a surface to the plane is irreducible, with only nodes and cusps.
The main result in this paper is as follows: Let S be the branch curve (in the projective plan) of a generic projection of a Veronese surface. Then the fundamental group of the complement of S is an extension of a solvable group by a symmetric group. A group with the property mentioned above is ``almost solvable'' in the sense that it contains a solvable normal subgroup of finite index. This raises the question for which families of simply connected algebraic surfaces of general type is the fundamental group of the complement of the branch curve of a generic projection to the complex plane an …
In this paper we give an asymptotic bound of the cardinality of Zariski multiples of particular plane singular curves. These curves have only nodes and cusps as singularities and are obtained as branched curves of ramified covering of the plane by surfaces isogenous to a product of curves with group $(\mathbb{Z}/2\mathbb{Z})^k$. The knowledge of the moduli space of these surfaces will enable us to produce Zariski multiplets whose number grows subexponentialy in function of their degree.
The topology of the generic polar curve and the Zariski invariant for branches of genus one
研究亏格为一的复平面分支的泛型极曲线拓扑型，基于值半群和Zariski不变量，改进Casas-Alvero 2023年的结果，通过Zariski不变量过滤分支的拓扑型。
This paper is the second in a series. The first one describes pillow degenerations of a $K3$ surface with genus $g$. In this paper we study the $(2,2)$-pillow degeneration of a non-prime $K3$ surface and the braid monodromy of the branch curve of the surface with respect to a generic projection onto $\C¶^2$. In future papers we study the fundamental group of the complement of the branch curve and the fundamental group of the Galois cover of the surface with respect to this generic projection.
In this paper, we compute the fundamental group of the complement of linear torus curves of maximal contact and we show that it is isomorphic that of generic linear torus curves.
In this paper we consider the problem of calculating the higher-order Weierstrass weight of the branch points of a superelliptic curve $C$. For any $q>1$, we give an exact formula for the $q$-weight of an affine branch point. We also find a formula for the $q$-weight of a point at infinity in the case where $n$ and $d$ are relatively prime. With these formulas, for any fixed $n$, we obtain an asymptotic formula for the ratio of the $q$-weight of the branch points, denoted $BW_q$, to the total $q$-weight of points on the curve: \[ \liminf_{d\to\infty}\frac{BW_q}{g(g-1)^2(2q-1)^2}\geq \frac{n+1}…
We construct infinitesimal deformations on an open domain of a smooth projective surface given by a complement of plumbings of disjoint linear chains of smooth rational curves. We show that the infinitesimal deformations are not small deformations, that is, they change the complex structure away from the boundary of the domain.
Hyperbolicity of Fermat-type curves and their complements
本文利用广义Borel定理证明了Fermat型曲线及其补集的双曲性，改进了现有度数界结果。
Homotopy type of complements of fiber-type curves
本文研究平面射影纤维型曲线补集的同伦型，在特定限制下给出完整描述，并部分肯定回答了 Libgober 关于补集同伦型是否由基本群和欧拉示性数决定的问题。
Let (A,L) be a principally polarized abelian surface of type (1,3). The linear system |L| defines a 6:1 covering of A onto P2, branched along a curve B of degree 18 in P2. The main result of the paper is that for general (A,L) the curve B irreducible, admits 72 cusps, 36 nodes or tacnodes, each tacnode counting as two nodes, 72 flexes and 36 bitangents. The main idea of the proof is to use the fact that for a general (A,L) of type (1,3) the closure of the Severi variety V in |L| is dual to the curve B in the sense of projective geometry. We investigate V and B via degeneration to a special abe…
Tropicalization of curve arrangement complements and arroids
本文引入 arroid 公理体系刻画曲线排列的交集性质，证明补集的热带化由 arroid 决定，并给出用热带上同调计算补集上同调及判定补集为极大簇的条件。
A plane curve is called strange if its tangent line at any smooth point passes through a fixed point, called the strange point. In this paper, we study $\mathbb{A}^1$-curves on the complement of a rational strange curve of degree $p$ in characteristic $p$. We prove the connectedness of the moduli spaces of $\mathbb{A}^1$-curves with given degree, classify their irreducible components, and exhibit the inseparable $\mathbb{A}^1$-connectedness via the $\mathbb{A}^1$-curves parameterized by each irreducible component. The key to these results is the strangeness of all $\mathbb{A}^1$-curves. As an …
Information Theoretic analysis of the periods of a hyperelliptic curve provides more information about the well--known but abstract relationship between the branch points and the periods. Here one constructs a canonical homology basis for a hyperelliptic curve that shows that its periods must satisfy certain constraints and defines an open set in the Siegel upper half space that cannot contain any period matrices of hyperelliptic curves.
Isomorphisms between complements of projective plane curves
本文研究射影平面不可约曲线补集间的同构，证明单尖点曲线补集同构蕴含射影等价，并推广至次数≤7的曲线，同时给出次数8的新反例。
We show that the isolated invariant branches globalize to algebraic curves, when we consider weak toric type complex hyperbolic foliations on projective toric ambient surfaces. To do it, we pass through a characterization of weak toric type foliations in terms of "non-degeneracy" conditions, associated to Newton polygons. We also give a description of the relationship between invariant algebraic curves and isolated invariant branches, valid for the case of toric type, by means of the following dichotomy. Either there is a rational first integral and there are no isolated invariant branches or …
Given two irreducible curves of the plane which have isomorphic complements, it is natural to ask whether there exists an automorphism of the plane that sends one curve on the other. This question has a positive answer for a large family of curves and H.Yoshihara conjectured that it is true in general. We exhibit counterexamples to this conjecture, over any ground field. In some of the cases, the curves are isomorphic and in others not; this provides counterexamples of two different kinds. Finally, we use our construction to find the existence of surprising non-linear automorphisms of affine s…
In 1984, H. Yoshihara conjectured that if two plane irreducible curves have isomorphic complements, they are projectively equivalent, and proved the conjecture for a special family of unicuspidal curves. Recently, J. Blanc gave counterexamples of degree 39 to this conjecture, but none of these is unicuspidal. In this text, we give a new family of counterexamples to the conjecture, all of them being unicuspidal, of degree 4m + 1 for any m \geq 2. In particular, we have counterexamples of degree 9, which seems to be the lowest possible degree.
An algorithm of Thomas Breuer produces complete lists of automorphism groups of curves for a fixed genus, and the code to execute this algorithm was written in the computer algebra package GAP and run by Breuer over a decade ago. For each curve $X$ of genus $g$ and a group $G$ acting on $X$, the branching data for the covering $X \to X/G$ is computed but was not record. We have added functionality to the code to output this data, and have translated the code to the computer algebra package Magma. This article provides an explanation of the code to add this branching data. Complete data from th…
In this paper, we give a fast algorithm for the computation of the Arf closure of an algebroid curve with more than one branch, generalizing an algorithm presented by Arslan and Sahin for the algebroid branch case.
The braid monodromy factorization of the branch curve of a surface of general type is known to be an invariant that completely determines the diffeomorphism type of the surface. Calculating this factorization is of high technical complexity; computing the braid monodromy factorization of branch curves of surfaces uncovers new facts and invariants of the surfaces. Since finding the branch curve of a surface is very difficult, we degenerate the surface into a union of planes. Thus, we can find the braid monodromy of the branch curve of the degenerated surface, which is a union of lines. The rege…
Fundamental groups of the complements to reducible curves on smooth surfaces with restricted classes of components
本文分类光滑单连通射影曲面上满足对偶簇次数≤6等奇异曲线束族，进而描述不可约分量为超平面截影类且基本群可满射到秩>6自由群的曲面上曲线补集的基本群。
This article describes the geometry of isomorphisms between complements of geometrically irreducible closed curves in the affine plane $\mathbb{A}^2$, over an arbitrary field, which do not extend to an automorphism of $\mathbb{A}^2$. We show that such isomorphisms are quite exceptional. In particular, they occur only when both curves are isomorphic to open subsets of the affine line $\mathbb{A}^1$, with the same number of complement points, over any field extension of the ground field. Moreover, the isomorphism is uniquely determined by one of the curves, up to left composition with an automor…
A criterion is given in order that the ideals of a one branch curve singularity form at most 2-parameter families. Namely, we present a list of plane curve singularities from the Arnold's classification which are the smallest among all one branch singularities having at most 2-parameter families of ideals.
We will describe the topological type of the discriminant curve of the morphism $(\ell, f)$, where $\ell$ is a smooth curve and $f$ is an irreducible curve (branch) of multiplicity less than five or a branch that the difference between its Milnor number and Tjurina number is less than 3. We prove that for a branch of these families, the topological type of the discriminant curve is determined by the semigroup, the Zariski invariant and at most two other analytical invariants of the branch.
The fundamental group of the complement of a generic fiber-type curve
本文刻画了无分量线束中有限多条一般纤维并集补集的基本群，指出其曾出现在 Eyral 和 Oka 的纤维型曲线例子中，并由此得到处理 Zariski 交换性问题的一个准则。
This paper will appear in the Santa Cruz proceedings. An overview of the braid group techniques in the theory of algebraic surfaces, from Zariski to the latest results, is presented. An outline of the Van Kampen algorithm for computing fundamental groups of complements of curves and the modification of Moishezon-Teicher regarding branch curves of generic projections are given. The paper also contains a description of a quotient of the braid group, namely $\tilde B_n$ which plays an important role in the description of fundamental groups of complements of branch curves.It turns out that all suc…
The present work is a user's guide to the results of a previous paper by the second and third authors, where a description of the space of characters of a quasi-projective variety was given in terms of global quotient orbifold pencils. Below we consider the case of plane curve complements and hyperplane arrangements. In particular, an infinite family of curves exhibiting characters of any torsion and depth~3 will be discussed. Also, in the context of line arrangements, it will be shown how geometric tools, such as the existence of orbifold pencils, can replace the group theoretical computation…
We study ramified covers of the projective plane. Given a smooth projective surface S and a generic enough projection of S to the projective plane, we get a cover of the plane ramified over a plane curve. The branch curve is usually singular, but is classically known to have only cusps and nodes as singularities for a generic projection. Several questions arise. First, what is the_geography_ of branch curves among all nodal-cuspidal curves? Second: what is the_geometry_ of branch curves? In other words, how can one distinguish a branch curve from a non-branch curve with the same numerical inva…
We construct new examples of singular projective plane curves whose complements have finite and non-abelian fundamental groups, by generalizing the classical three cuspidal quartic curve discovered by Zariski.
An efficient algorithm for computing the branching structure of a compact Riemann surface defined via an algebraic curve is presented. Generators of the fundamental group of the base of the ramified covering punctured at the discriminant points of the curve are constructed via a minimal spanning tree of the discriminant points. This leads to paths of minimal length between the points, which is important for a later stage where these paths are used as integration contours to compute periods of the surface. The branching structure of the surface is obtained by analytically continuing the roots o…
Computing Jet Differentials and the Green-Griffiths-Lang Conjecture for Complements of Smooth Plane Curves
针对光滑平面曲线补集的Green-Griffiths-Lang猜想，本文开发了计算负扭曲不变对数2-喷流微分族的有效方法，给出该猜想的计算准则并对若干曲线族验证，明确了相关例外轨迹。
We study the cohomology jump loci of rank one local systems for the plane curve germ complement by the deletion restriction method. In particular, the deletion restriction type results in this case only depend on the linking numbers between the irreducible components of the plane curve germ.
Recovery of Plane Curves from Branch Points
本文研究从分支点恢复三次和四次平面曲线的问题，利用平面Hurwitz数刻画解轨道数，确定实数解个数，并基于经典代数几何给出精确恢复算法。
The amoeba of a complex curve in the 2-dimensional complex torus is its image under the projection onto the real subspace in the logarithmic scale. The complement to an amoeba is a disjoint union of connected components that are open and convex. A toric cycle is a 2-cycle in the complement to a curve associated with a component of the complement to an amoeba. We prove homological independence of toric cycles in the complement to a complex algebraic curve with amoeba of maximal area.
We formulate and prove a weighted version of Zariski's hyperplane section theorem on the topological fundamental groups of the complements of hypersurfaces in a projective space. As an application, we calculate fundamental groups of the complements of certain singular projective plane curves.
The paper is a contribution of the conjecture of Kobayashi that the complement of a generic plain curve of degree at least five is hyperbolic. The main result is that the complement of a generic configuration of three quadrics is hyperbolic and hyperbolically embedded as well as the complement of two quadrics and a line.
We use the Krammer representation of the braid group in Libgober's invariant and construct a new multivariate polynomial invariant for curve complements: Krammer polynomial. We show that the Krammer polynomial of an essential braid is equal to zero. We also compute the Krammer polynomials of some certain n-gonal curves.
The reciprocal complement of a curve
该研究针对代数闭域上一维有限生成代数的整环D，给出了整环互反补的几何解释，属于代数与代数几何领域的理论研究。
Handle decompositions and Kirby diagrams for the complement of plane algebraic curves
本文基于辫形monodromy概念，研究平面代数曲线补集的显式处理分解和Kirby图，提出改进的技巧以获得相关结构。
For a convenient and Newton non-degenerate singularity, the Milnor number is computed from the complement of its Newton diagram in the first quadrant, so-called Kouchnirenko's formula. In this paper, we consider tropical curves dual to subdivisions of this complement for a plane curve singularity and show the existence of a tropical curve satisfying a certain formula, which looks like a well-known formula for a real morsification due to A'Campo and Gusein-Zade.
The paper reviews recent developments in the study of Alexander invariants of quasi-projective manifolds using methods of singularity theory. Several results in topology of the complements to singular plane curves and hypersurfaces in projective space extended to the case of curves on simply connected smooth projective surfaces.
We study smooth curves on abelian surfaces, especially for genus 4, when the complementary subvariety in the Jacobian is also a surface. We show that up to translation there is exactly one genus 4 hyperelliptic curve on a general (1, 3)-polarised abelian surface. We investigate these curves and show that their Jacobians contain a surface and its dual as complementary abelian subvarieties.
Constructions for rational multiple planes
本文在适当一般条件下，分类了更简单的三重平面，且给出了无限多个非克雷莫纳等价的更高倍数平面家族的例子。
We introduce the notion of an approximate jacobian Newton diagram which is the jacobian Newton diagram of the morphism $(f^{(k)},f)$, where $f$ is a branch and $f^{(k)}$ is a characteristic approximate root of $f$. We prove that the set of all approximate jacobian Newton diagrams is a complete topological invariant. This generalizes theorems of Merle and Ephraim about the decomposition of the polar curve of a branch.
For a smooth plane cubic $B$, we count curves $C$ of degree $d$ such that the normalizations of $C\backslash B$ are isomorphic to $\Bbb A^1$, for $d\leq7$ (for $d=7$ under some assumption). We also count plane rational quartic curves intersecting $B$ at only one point.
We classify the log del Pezzo surface (S,B) of rank 1 with no 1-,2-,3-,4-, or 6-complements with the additional condition that B has one irreducible component C which is an elliptic curve, and that C has the coefficient b in B with (1/n)floor((n+1)b)=1 for n=1,2,3,4, and 6.
The paper is a contribution to the conjecture of Kobayashi that the complement of a generic curve in the projective plane is hyperbolic, provided the degree is at least five. Previously the authors treated the cases of two quadrics and a line and three quadrics. The main results are Let C be the union of three curves in P_2 whose degrees are at least two, one of which is at least three. Then for generic such configurations the complement of C is hyperbolic and hyperbolically embedded. The same statement holds for complements of curves in generic hypersurfaces X of degree at least five and curv…
In this paper we discuss some properties of fundamental groups and Alexander polynomials of plane curves. We discuss the relationship of the non-triviality of Alexander polynomials and the notion of (nearly) freeness for irreducible plane curves. We reprove and restate in modern terms a somewhat forgotten result of Zariski. Finally, we describe some topological properties of curves with abelian fundamental group.
We discuss the applications of fundamental groups (of complements of curves) computations (and possibly the computations of the second homotopy group as a model over it) to the classification of algebraic surface. We prove that the fundamental group of the complement of the branch curve of a generic projection of a Veronese surface to the complex plane is an "almost solvable" group in the sense that it contains a solvable group of finite index and thus we can consider the second fundamental group as model over the first.
Let ${\mathcal {B}}$ be a reducible reduced plane curve. We introduce a new point of view to study the topology of $(\PP^2, {\mathcal {B}})$ via Galois covers and Alexander polynomials. We show its effectiveness through examples of Zariski $N$-plets for conic and conic-quartic configurations.
Curves on irrational ruled surfaces whose complements are of non-general type
研究无理直纹曲面上曲线补集的对数Kodaira维数，给出其等于K_X+B的Iitaka维数的证明，并分类维数小于2时的曲线配置，以及维数为1时对数多重典范系统的结构。
An origami (also known as square-tiled surface) is a Riemann surface covering a torus with at most one branch point. Lifting two generators of the fundamental group of the punctured torus decomposes the surface into finitely many unit squares. By varying the complex structure of the torus one obtains easily accessible examples of Teichmüller curves in the moduli space of Riemann surfaces. The p-adic analogues of Riemann surfaces are Mumford curves. A p-adic origami is defined as a covering of Mumford curves with at most one branch point, where the bottom curve has genus one. A classification o…
Exceptional Loci and Hyperbolicity of Complements of Plane Curves with $\bar{c}_1^2 - \bar{c}_2 > 0$
本文证明满足特定次数条件的一般平面曲线，其代数例外集为空，进而得出满足 $\bar{c}_1^2 - \bar{c}_2 > 0$ 的平面曲线补集是 Kobayashi 双曲的。
This is an introduction to topology of complement to plane curves and hypersurfaces in the projective space and is based on the lectures given in Lumini in February and in ICTP (Trieste) in August of 2005. We discuss key problems concerning the families of singular curves, the one variable Alexander polynomials and the module over ring of Laurent polynomials structure on the homotopy groups of the complements to hypersurfaces with isolated singularities. We also discuss multivariable generalizations of these invariants and the Hodge theory of infinite abelian covers used in calculations of mul…
The general problem which initiated this work is: What are the quasiprojective varieties which can be uniformized by means of bounded domains in $\cz^n$ ? Such a variety should be, in particular, C--hyperbolic, i.e. it should have a Carathéodory hyperbolic covering. We study here the plane projective curves whose complements are C--hyperbolic. For instance, we show that most of the curves whose duals are nodal or, more generally, immersed curves, belong to this class. We also give explicit examples of irreducible such curves of any even degree d greater or equal 6.
The purpose of this paper is two-fold. We first prove a series of results, concerned with the notion of Zariski multiplicity, mainly for non-singular algebraic curves. These results are required in the paper "A Theory of Branches for Algebraic Curves",(*), where, following Severi, we introduced the notion of the "branch" of an algebraic curve. Secondly, we use results from the cited paper, (*), in order to develop a refined theory of g_{n}^{r} on an algebraic curve. The refinement depends critically on relacing the notion of a point with a branch. This allows us to construct a theory of diviso…
In this paper we show that in a stable range the cohomology of the space of regular algebraic sections of a line bundle $\mathscr{L}$on a curve $X$ is isomorphic to the cohomology of the space of regular $C^{\infty}$sections of the same line bundle.
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