A note on families of hyperelliptic curves

A Note on a Brill-Noether Locus over a Non-hyperelliptic curve of genus 4

We prove that a certain Brill-Noether locus over a non-hyperelliptic curve $C$ of genus 4, is isomorphic to the \textit{Donagi-Izadi cubic threefold} in the case when the pencils of the two trigonal line bundles of $C$ coincide.

The 2-Weierstrass points of genus 3 hyperelliptic curves with extra automorphisms

For each group $G$, $(|G| > 2)$ \, which acts as a full automorphism group on a genus 3 hyperelliptic curve, we determine the family of curves which have 2-Weierstrass points. Such families of curves are explicitly determined in terms of the absolute invariants of binary octavics. The 1-dimensional families that we discover have the property that they contain only genus 0 components.

Notes on hyperelliptic fibrations of genus 3, II

This is the part II of the series under the same title. In part I, using the approach developed by Catanese--Pignatelli arXiv:math/0503294, we gave a structure theorem for hyperelliptic genus 3 fibrations all of whose fibers are 2-connected (arXiv:1209.6278 [math.AG]). In this part II, we shall give a structure theorem for smooth deformation families of these to non-hyperelliptic genus 3 fibrations. As an application, we shall give a set of sufficient conditions for our genus 3 hyperelliptic fibration above to allow deformation to non-hyperelliptic fibrations, and use this to study certain min…

Families of absolutely simple hyperelliptic jacobians

We prove that the jacobian of a hyperelliptic curve $y^2=(x-t)h(x)$ has no nontrivial endomorphisms over an algebraic closure of the ground field $K$ of characteristic zero if $t \in K$ and the Galois group of the polynomial $h(x)$ over $K$ is "very big" and $deg(h)$ is an even number >8. (The case of odd $deg(h)>3$ follows easily from previous results of the author.)

Algebraic families of hyperelliptic curves violating the Hasse principle

In $2000$, Colliot-Thélène and Poonen showed how to construct algebraic families of genus one curves violating the Hasse principle. Poonen explicitly constructed an algebraic family of genus one cubic curves violating the Hasse principle using the general method developed by Colliot-Thélène and himself. The main result in this paper generalizes the result of Colliot-Thélène and Poonen to arbitrarily high genus hyperelliptic curves. More precisely, for $n > 5$ and $n \not\equiv 0 \pmod{4}$, we show that there is an algebraic family of hyperelliptic curves of genus $n$ that is counterexamples to…

A note on Shimura subvarieties in the hyperelliptic Torelli locus

We prove the non-existence of Shimura subvarieties of positive dimension contained generically in the hyperelliptic Torelli locus for curves of genus at least 8, which is an analogue of Oort's conjecture in the hyperelliptic case.

次数为4的del Pezzo曲面与亏格模4余1的超椭圆曲线的代数族违反Hasse原则

Hasse principle violation for algebraic families of del Pezzo surfaces of degree 4 and hyperelliptic curves of genus congruent to 1 modulo 4

本文构造了无限多个显式单参数代数族，包含次数为4的del Pezzo曲面和亏格模4余1的超椭圆曲线，证明其每个K成员都违反Hasse原则，并由Brauer-Manin障碍解释。

Notes on hyperelliptic fibrations of genus 3, I

We shall study the structure of hyperelliptic fibrations of genus 3, from the view point given by Catanese and Pignatelli in arXiv:math/0503294. In this part I, we shall give a structure theorem for such fibrations for the case of f : S \to B with all fibers 2-connected. We shall also give, for the case of B projective line, sufficient conditions for the existence of such fibrations from the view point of our structure theorem, prove the uniqueness of the deformation type and the simply connectedness of S for some cases, and give some examples including those with minimal regular S with geomet…

A Short Note on Self-Duality of Goppa Codes on Elliptic and Hyperelliptic Function Fields

In this note, we investigate Goppa codes which are constructed by means of Elliptic function field and Hyperelliptic function field. We also give a simple criterion for self-duality of these codes.

超椭圆曲线的一些特殊族

Some special families of hyperelliptic curves

本文研究具有指定自同构子群的亏格 g 超椭圆曲线轨迹，证明两类循环情形的有理性并给出函数域生成元，另对两类非循环群给出判别条件及 g≤12 时模域即定义域的结论。

Point counting in families of hyperelliptic curves in characteristic 2

Let E_G be a family of hyperelliptic curves over F2^(alg cl) with general Weierstrass equation given over a very small field F. We describe in this paper an algorithm to compute the zeta function of E_g for g in a degree n extension field of F, which has as time complexity O(n^3) and memory requirements O(n^2). With a slightly different algorithm we can get time O(n^2,667) and memory O(n^2,5), and the computation of O(n) curves of the family can be done in time and space O(n^3). All these algorithms are polynomial in the genus.

On the Mahler measure of hyperelliptic families

We prove Boyd's "unexpected coincidence" of the Mahler measures for two families of two-variate polynomials defining curves of genus 2. We further equate the same measures to the Mahler measures of polynomials $y^3-y+x^3-x+kxy$ whose zero loci define elliptic curves for $k\ne0,\pm3$.

Point counting in families of hyperelliptic curves

Let E_G be a family of hyperelliptic curves defined by Y^2=Q(X,G), where Q is defined over a small finite field of odd characteristic. Then with g in an extension degree n field over this small field, we present a deterministic algorithm for computing the zeta function of the curve E_g by using Dwork deformation in rigid cohomology. The time complexity of the algorithm is O(n^(2.667)) and it needs O(n^(2.5)) bits of memory. A slight adaptation requires only O(n^2) space, but costs time O(n^3). An implementation of this last result turns out to be quite efficient for n big enough.

超椭圆族与四维$\u003cspan style="font-family: calibri"\u003eN\u003c/span\u003e=2超共形场论

Hyperelliptic families and 4d $\mathcal{N}=2$ SCFT

本研究对SW几何可表为超椭圆族的四维N=2超共形场论分类，借助特殊凯勒条件简化问题，通过孤立奇点约束得到分类结果，给出完整SW几何与微分，复现已知结果并给出任意秩无穷序列，还研究了Z₂商及推广方向。

Average size of 2-Selmer groups of Jacobians of hyperelliptic curves over function fields

In this paper, we are going to compute the average size of 2-Selmer groups of two families of hyperelliptic curves with marked points over function fields. The result will be obtained by a geometric method which could be considered as a generalization of the one that was used previously by Q.P. Ho, V.B. Le Hung, and B.C. Ngo to obtain the average size of 2-Selmer groups of elliptic curves.

Representations of divisors on hyperelliptic curves, Gröbner bases and plane curves with quasi-toric relations

In the study of hyperelliptic curve cryptography, presentations of semi-reduced divisors on a hyperelliptic curve play important roles. In this note, we give an interpretation for such presentations from view points of Gröbner bases. As applications, (i) we give a method to construct weak $n$-contact curves and (ii) we study plane curves satisfying quasi-toric relations of type $(2, n, 2)$

关于超椭圆映射类群的注记

Notes on hyperelliptic mapping class groups

本文系统研究超椭圆映射类群，给出Putman-Wieland猜想在亏格2情形的反例，并将同余子群性质推广到一般超椭圆映射类群，确定其profinite完备化中多重扭转和开子群的中心化子。

Statistics of the zeros of zeta functions in families of hyperelliptic curves over a finite field

We study the fluctuations in the distribution of zeros of zeta functions of a family of hyperelliptic curves defined over a fixed finite field, in the limit of large genus. According to the Riemann Hypothesis for curves, the zeros all lie on a circle. Their angles are uniformly distributed, so for a curve of genus g a fixed interval I will contain 2g|I| angles as the genus grows. We show that for the variance of number of angles in I is asymptotically a constant multiple of log(2g|I|) and prove a central limit theorem: The normalized fluctuations are Gaussian. These results continue to hold fo…

Two-dimensional families of hyperelliptic jacobians with big monodromy

Let $K$ be a global field of characteristic different from 2 and $u(x)\in K[x]$ be an irreducible polynomial of even degree $2g\ge 6$, whose Galois group over $K$ is either the full symmetric group $S_{2g}$ or the alternating group $A_{2g}$. We describe explicitly how to choose (infinitely many) pairs of distinct elements $t_1, t_2$ of $K$ such that the $g$-dimensional jacobian of a hyperelliptic curve $y^2=(x-t_1)(x-t_2))u(x)$ has no nontrivial endomorphisms over an algebraic closure of $K$ and has big $\ell$-adic monodromy.

On Abel's hyperelliptic curves

In this note we discuss a class of hyperelliptic curves introduced by Abel in a 1826 paper. After some indications of the context in which he introduced them and a description of his main result we give some results on the moduli space of such curves. In particular we compute the dimension of it at each of its points as well as giving a combinatorial formula for the number of components.

Hyperelliptic Curves with Maximal Galois Action on the Torsion Points of their Jacobians

In this article, we show that in each of four standard families of hyperelliptic curves, there is a density-$1$ subset of members with the property that their Jacobians have adelic Galois representation with image as large as possible. This result constitutes an explicit application of a general theorem on arbitrary rational families of abelian varieties to the case of families of Jacobians of hyperelliptic curves. Furthermore, we provide explicit examples of hyperelliptic curves of genus $2$ and $3$ over $\mathbb Q$ whose Jacobians have such maximal adelic Galois representations.

Hyperelliptic Curves with Prescribed $p$-Torsion

In this paper, we show that there exist families of curves (defined over an algebraically closed field $k$ of characteristic $p >2$) whose Jacobians have interesting $p$-torsion. For example, for every $0 \leq f \leq g$, we find the dimension of the locus of hyperelliptic curves of genus $g$ with $p$-rank at most $f$. We also produce families of curves so that the $p$-torsion of the Jacobian of each fibre contains multiple copies of the group scheme $α_p$. The method is to study curves which admit an action by $(\ZZ/2)^n$ so that the quotient is a projective line. As a result, some of these fa…

Families of supersingular curves in characteristic 2

This paper determines the normal forms of hyperelliptic supersingular curves of genus g over an algebraically closed field F of characteristic 2 for 0 < g< 9. We also show that every hyperelliptic supersingular curve of genus 9 over F has an equation y^2-y=x^19+c^8x^9+c^3x for some c in F_2bar. The paper determines the dimensions of the open locus of hyperelliptic supersingular curves of genus g < 10 over F_2bar.

Faltings' delta-invariant of a hyperelliptic Riemann surface

In this note we give a closed formula for Faltings' delta-invariant of a hyperelliptic Riemann surface.

一般的单参数超椭圆族是稠密的

Generically Ordinary One-parameter Hyperelliptic Families are Dense

该论文研究d>4的单参数超椭圆族的约化性质，证明扎里斯基一般系数对应的超椭圆族在大素数处有一般平凡约化，且平凡素数的自然密度在基变换后为1。

A note on local trigonal fibrations

We show that some of centeral fibers of degenerations of hyperelliptic curves are realized as those trigonal curves. In particular, any hyperelliptic curve can be the central fiber of a degeneration of trigonal curves.

超椭圆曲线、扫描映射与二次L函数族的矩

Hyperelliptic curves, the scanning map, and moments of families of quadratic L-functions

计算辫子群在应用于积分约化Burau表示的任何Schur函子中的稳定同调，这是带扭曲系数的Mumford猜想的超椭圆类似物，还将结果与二次L函数族矩的猜想联系起来，证实了相关预测。

Subvarieties of the hyperelliptic moduli determined by group actions

Let $\mathcal H_g$ be the moduli space of genus $g$ hyperelliptic curves. In this note, we study the locus $\mathcal L$ in $\mathcal H_g$ of curves admitting a $G$-action of given ramification type $σ$ and inclusions between such loci. For each genus we determine the list of all possible groups, the inclusions among the loci, and the corresponding equations of the generic curve in $\mathcal L$. The proof of the results is based solely on representations of finite subgroups of $PGL_2 (\mathbb C)$ and the Riemann-Hurwitz formula.

可分解 Jacobian 的显式构造

Explicit construction of decomposable Jacobians

本文给出了特征0域上可分解超椭圆 Jacobian 簇的显式构造，并应用于构造具有无穷多二次扭转且含有有理非 Weierstrass 点的超椭圆曲线族。

Springer correspondence, hyperelliptic curves, and cohomology of Fano varieties

In \cite{CVX3}, we have established a Springer theory for the symmetric pair $(\operatorname{SL}(N),\operatorname{SO}(N))$. In this setting we obtain representations of (the Tits extension) of the braid group rather than just Weyl group representations. These representations arise from cohomology of families of certain (Hessenberg) varieties. In this paper we determine the Springer correspondence explicitly for IC sheaves supported on order 2 nilpotent orbits. In this process we encounter universal families of hyperelliptic curves. As an application we calculate the cohomolgy of Fano varieties…

超椭圆稳定曲线

Hyperelliptic Stable Curves

本文给出了亏格≥2的超椭圆稳定曲线的内在刻画，通过分析对合作用及节点分解，得到超椭圆性的显式结构描述，并证明了对合的唯一性，适用于任意特征，精确捕捉了特征2中的特殊行为。

On families of rational curves in the Hilbert square of a surface (with an Appendix by Edoardo Sernesi)

Under natural hypotheses we give an upper bound on the dimension of families of singular curves with hyperelliptic normalizations on a surface S with p_g(S) >0 via the study of the associated families of rational curves in Hilb^2(S). We use this result to prove the existence of nodal curves of geometric genus 3 with hyperelliptic normalizations, on a general K3 surface, thus obtaining specific 2-dimensional families of rational curves in its Hilbert square. We describe two infinite series of examples of general, primitively polarized K3's such that their Hilbert squares contain a IP^2 or a thr…

Families of n-gonal curves with maximal variation of moduli

We study families of n-gonal curves with maximal variation of moduli, which have a rational section. Certain numerical results on the degree of the modular map are obtained for such families of hyperelliptic and trigonal curves. In the last case we use the description of the relative Picard group of the universal family of trigonal curves.

超椭圆曲线的普通族构造

Construction of Generically Ordinary Families of Hyperelliptic Curves

本文证明对于每个g≥2和非零代数整数α，超椭圆曲线族y²=x^d+αx+t在满足一定条件下在几乎所有素数p处是普通族，改进了Katz的猜想。

Vanishing thetanulls on curves with involutions

The configuration of theta characteristics and vanishing thetanulls on a hyperelliptic curve is completely understood. We observe in this note that analogous results hold for the s-invariant theta characteristics on any curve C with an involution s . As a consequence we get examples of non hyperelliptic curves with a high number of vanishing thetanulls.

有限域上由椭圆曲线和超椭圆曲线得到的极大奇异曲线

Maximal singular curves over finite fields from elliptic and hyperelliptic curves

本文构造有限域上达到Aubry-Perret界的极大奇异曲线族，利用椭圆/超椭圆曲线的线性投影和Gorenstein曲线理论，并确定所得曲线的gonality。

$K$-weight bounds for $γ$-hyperelliptic semigroups

In this note, we show that {\it $γ$-hyperelliptic} numerical semigroups of genus $g \gg γ$ satisfy a refinement of a well-known characteristic weight inequality due to Torres. The refinement arises from substituting the usual notion of weight by an alternative version, the $K$-weight, which we previously introduced in the course of our study of unibranch curve singularities.

超椭圆曲线在K3表面上的雅可比矩阵秩跃迁

Rank jumps for Jacobians of Hyperelliptic curves on K3 surfaces

研究数域上K3表面超椭圆曲线雅可比矩阵秩跃迁现象，证明有限扩展下秩跃迁无限集的存在，并描述K3表面几何条件下的非薄纤维秩跃迁。

Numerical verification of Beilinson's conjecture for K2 of hyperelliptic curves

We construct families of hyperelliptic curves over Q of arbitrary genus g with (at least) g integral elements in K_2. We also verify the Beilinson conjectures about K_2 numerically for several curves with g=2, 3, 4 and 5. The paper is essentially self-contained and may serve as an elementary introduction to Beilinson's conjectures for K_2 of curves.

Determining the automorphism group of a hyperelliptic curve

In this note we discuss techniques for determining the automorphism group of a genus $g$ hyperelliptic curve $\X_g$ defined over an algebraically closed field $k$ of characteristic zero. The first technique uses the classical $GL_2 (k)$-invariants of binary forms. This is a practical method for curves of small genus, but has limitations as the genus increases, due to the fact that such invariants are not known for large genus. The second approach, which uses dihedral invariants of hyperelliptic curves, is a very convenient method and works well in all genera. First we define the normal decompo…

Efficiently computable endomorphisms for hyperelliptic curves

Elliptic curves have a well-known and explicit theory for the construction and application of endomorphisms, which can be applied to improve performance in scalar multiplication. Recent work has extended these techniques to hyperelliptic Jacobians, but one obstruction is the lack of explicit models of curves together with an efficiently computable endomorphism. In the case of hyperelliptic curves there are limited examples, most methods focusing on special CM curves or curves defined over a small field. In this article we describe three infinite families of curves which admit an efficiently co…

The field of meromorphic functions on a sigma divisor of a hyperelliptic curve of genus 3 and applications

The field of meromorphic functions on a sigma divisor of a hyperelliptic curve of genus $3$ is described in terms of the gradient of it's sigma function. Solutions of corresponding families of polynomial dynamical systems in $\mathbb{C}^4$ with two polynomial integrals are constructed as an application. These systems were introduced in the work of V. M. Buchstaber and A. V. Mikhailov on the basis of commuting vector fields on the symmetric square of algebraic curves.

A Note on a Conjecture of Xiao

Let f:S ->B be a relatively minimal fibred surface. In this note we give a partial affirmative answer to a conjecture of Xiao, proving that the direct image of the relative dualizing sheaf of $f$ is ample when the slope of the fibration is less than 4, if the general fibre of $f$ is non-hyperelliptic or the genus of the fibre or of the base curve is low.

具有极大 Galois 像的超椭圆 Jacobian 乘积

Products of hyperelliptic Jacobians with maximal Galois image

本文研究了超椭圆 Jacobian 乘积的相伴 adelic 表示，给出了确保其具有极大 Galois 像的简单准则，并提出了一种构造 Jacobian 乘积使其除法域尽可能互不相交的方法。

Eigenforms of hyperelliptic curves with many automorphisms

Given a pair of translation surfaces it is very difficult to determine whether they are supported on the same algebraic curve. In fact, there are very few examples of such pairs. In this note we present infinitely many examples of finite collections of translation surfaces supported on the same algebraic curve. The underlying curves are hyperelliptic curves with many automorphisms. For each curve, the automorphism of maximal order acts on the space of holomorphic 1-forms. We present a translation surface corresponding to each of the eigenforms of this action.

Fiber products of hyperelliptic curves

Let $k$ be a number field, and let $S$ be a finite set of maximal ideals of the ring of integers of $k$. In his 1962 ICM address, Shafarevich asked if there are only finitely many $k$-isomorphism classes of algebraic curves of a fixed genus $g\ge 1$ with good reduction outside $S$. He verified this for $g=1$ by reducing the problem to Siegel's theorem. Parshin extended this argument to all hyperelliptic curves (cf. also the work of Oort). The general case was settled by Faltings' celebrated work. In this note we give a short proof of Shafarevich's conjecture for hyperelliptic curves, by reduci…

The Scorza correspondence in genus 3

In this note we prove the genus 3 case of a conjecture of G. Farkas and A. Verra on the limit of the Scorza correspondence for curves with a theta-null. Specifically, we show that the limit of the Scorza correspondence for a hyperelliptic genus 3 curve C is the union of the curve ${x,σ(x))$ (where $σ$ is the hyperelliptic involution), and twice the diagonal. Our proof uses the geometry of the subsystem Γ_{00} of the linear system 2Θ, and Riemann identities for theta constants.

一维族中非一般曲线的质量公式

Mass formula for non-ordinary curves in one dimensional families

本文研究正特征下射影直线循环覆盖一维族中非一般曲线的质量公式，通过tautological intersection theory和$a$-numbers证明两个方程，推广了Eichler--Deuring等人的结果并在超椭圆曲线等新情形下确定了公式。

Hyperelliptic curves, continued fractions, and Somos sequences

We detail the continued fraction expansion of the square root of a monic polynomials of even degree. We note that each step of the expansion corresponds to addition of the divisor at infinity, and interpret the data yielded by the general expansion. In the quartic and sextic cases we observe explicitly that the parameters appearing in the continued fraction expansion yield integer sequences defined by bilinear relations instancing sequences of Somos type.

A geometric interpretation and a new proof of a relation by Cornalba and Harris

In the 80's M. Cornalba and J. Harris discovered a relation among the Hodge class and the boundary classes in the Picard group with rational coefficients of the moduli space of stable, hyperelliptic curves. They proved the relation by computing degrees of the classes involved for suitable one-parameter families. In the present article we show that their relation can be obtained as the class of an appropriate, geometrically meaningful empty set, thus conforming with C. Faber's general philosophy to finding relations among tautological classes in the Chow ring of the moduli space of curves. The …

一般双有理性与超椭圆Theta除子

General birationality and Hyperelliptic Theta divisors

本文提出了确保双有理映射为开性质及一般双有理性的准则，并利用超椭圆曲线Jacobian的Theta除子研究，证明了非主极化超曲面的典范映射双有理性。

关于一些超椭圆 Hurwitz-Hodge 积分

On some hyperelliptic Hurwitz-Hodge integrals

本文针对超椭圆轨迹上的 Hurwitz-Hodge 单后裔积分，利用自旋结构 Chern 类与 Eynard-Orantin 拓扑递归关系，给出其为 Stirling 数的简洁新证明，并指出三类推广方向。

Some explicit elliptic modular surfaces

We consider algebraic surfaces, recently constructed by Schreieder, that are smooth models of the quotient of the self-product of a complex hyperelliptic curve by a $(\mathbb{Z}/3^c\mathbb{Z})$-action. We show that these surfaces are elliptic modular surfaces in the sense of Shioda, meaning in particular that they are universal families of explicit moduli of elliptic curves.

一个正比例的亏格 $g \geq 4$ 的首一奇次数超椭圆曲线没有意外的二次点

A positive proportion of monic odd-degree hyperelliptic curves of genus $g \geq 4$ have no unexpected quadratic points

本文证明对每个亏格 $g\geq 4$，正比例的首一奇次数超椭圆曲线除拉回点外无二次点，推广了 Poonen-Stoll 关于有理点的结果。