Decomposed Richelot isogenies of Jacobian varieties of curves of genus 3

Hyperelliptic Jacobians and isogenies

Motivated by results of Mestre and Voisin, in this note we mainly consider abelian varieties isogenous to hyperelliptic Jacobians In the first part we prove that a very general hyperelliptic Jacobian of genus $g\ge 4$ is not isogenous to a non-hyperelliptic Jacobian. As a consequence we obtain that the Intermediate Jacobian of a very general cubic threefold is not isogenous to a Jacobian. Another corollary tells that the Jacobian of a very general $d$-gonal curve of genus $g \ge 4$ is not isogenous to a different Jacobian. In the second part we consider a closed subvariety $\mathcal Y \subset …

Translating the discrete logarithm problem on Jacobians of genus 3 hyperelliptic curves with $(\ell,\ell,\ell)$-isogenies

We give an algorithm to compute $(\ell,\ell,\ell)$-isogenies from the Jacobians of genus three hyperelliptic curves to the Jacobians of non-hyperelliptic curves. An important application is to reduce the discrete logarithm problem in the Jacobian of a hyperelliptic curve to the corresponding problem in the Jacobian of a non-hyperelliptic curve.

Computing isogenies between jacobians of hyperelliptic curves of arbitrary genus via differential equations

Let $p$ be an odd prime number and be an integer coprime to $p$. We survey an algorithm for computing explicit rational representations of $(\ell,...,\ell)$-isogenies between Jacobians of hyperelliptic curves of arbitrary genus over an extension $K$ of the field of $p$-adic numbers $\mathbb{Q}\_p$. The algorithm has a quasi-linear complexity in $\ell$ as well as in the genus of the curves.

利用 Richelot 同构图列出亏格三的超特殊曲线

Listing superspecial curves of genus three using Richelot isogeny graphs

本文提出一种利用 theta 函数计算维数 3 超特殊主极化阿贝尔簇 Richelot isogeny graph 的显式算法，实现了超特殊亏格 3 曲线的高效枚举，并统计了 $11 \leq p < 100$ 时其中超椭圆曲线的数量。

On isogenies among certain abelian surfaces

We construct a three-parameter family of non-hyperelliptic and bielliptic plane genus-three curves whose associated Prym variety is two-isogenous to the Jacobian variety of a general hyperelliptic genus-two curve. Our construction is based on the existence of special elliptic fibrations with the section on the associated Kummer surfaces that provide a simple geometric interpretation for the rational double cover induced by the two-isogeny between the abelian surfaces.

亏格3曲线的一些显式算术及其应用

Some explicit arithmetic on curves of genus three and their applications

本文发展了亏格3曲线的显式算术，提出了计算分解Richelot同源余域的算法及Howe曲线定义方程的显式公式，并据此构建了枚举超特殊Howe曲线的高效算法。

Computing functions on Jacobians and their quotients

We show how to efficiently compute functions on jacobian varieties and their quotients. We deduce a quasi-optimal algorithm to compute $(l,l)$ isogenies between jacobians of genus two curves.

Fast computation of hyperelliptic curve isogenies in odd characteristic

Let p be an odd prime number and g $\ge$ 2 be an integer. We present an algorithm for computing explicit rational representations of isogenies between Jacobians of hyperelliptic curves of genus g over an extension K of the field of p-adic numbers Qp. It relies on an efficient resolution, with a logarithmic loss of p-adic precision, of a first order system of differential equations.

On isogenous principally polarized abelian surfaces

We study a relationship between two genus 2 curves whose jacobians are isogenous with kernel equal to a maximal isotropic subspace of p-torsion points with respect to the Weil pairing. For p = 3 we find an explicit relationship between the set of Weierstrass points of the two curves extending the classical results of F. Richelot (1837) and G. Humbert (1901) in the case p = 2.

Curves, Jacobians, and Cryptography

The main purpose of this paper is to give an overview over the theory of abelian varieties, with main focus on Jacobian varieties of curves reaching from well-known results till to latest developments and their usage in cryptography. In the first part we provide the necessary mathematical background on abelian varieties, their torsion points, Honda-Tate theory, Galois representations, with emphasis on Jacobian varieties and hyperelliptic Jacobians. In the second part we focus on applications of abelian varieties on cryptography and treating separately, elliptic curve cryptography, genus 2 and …

Prym varieties and fourfold covers

We describe the isotypical decomposition of the Jacobian variety JW of the Galois extension W-->T of any fourfold cover of smooth connected irreducible projective complex curves X-->T, in terms of Prym's of intermediate covers. We also compute the degree of the isogenies involved and as a result we obtain new proofs of the bigonal and trigonal constructions. Furthermore, we give examples of families of Jacobians isogenous to a product of Jacobians and of families of Prym varieties isogenous to the product of elliptic curves.

The arithmetic-geometric mean and isogenies for curves of higher genus

Computation of Gauss's arithmetic-geometric mean involves iteration of a simple step, whose algebro-geometric interpretation is the construction of an elliptic curve isogenous to a given one, specifically one whose period is double the original period. A higher genus analogue should involve the explicit construction of a curve whose jacobian is isogenous to the jacobian of a given curve. The doubling of the period matrix means that the kernel of the isogeny should be a lagrangian subgroup of the group of points of order 2 in the jacobian. In genus 2 such a construction was given classically by…

A tower of genus 2 curves related to the Kowalewski top

Several curves of genus 2 are known, such that the equations of motion of the Kowalewski top are linearized on their Jacobians. One can expect from transcendental approaches via solutions of equations of motion in theta-functions, that their Jacobians are isogeneous. The paper focuses on two such curves: Kowalewski's and that of Bobenko-Reyman-Semenov-Tian-Shansky, the latter arising from the solution of the problem by the method of spectral curves. An isogeny is established between the Jacobians of these curves by purely algebraic means, using Richelot's transformation of a genus 2 curve. It …

从亏格2的模方程计算同源

Computing isogenies from modular equations in genus two

提出一种算法，利用模方程和显式Kodaira-Spencer同构，在特征足够大且曲线足够一般的条件下，显式计算亏格2曲线上Jacobian的l-同源或循环核同源。

从超椭圆曲线到超椭圆曲线

From hyperelliptic to superelliptic curves

本文综述了将椭圆与超椭圆曲线理论推广到所有超椭圆曲线的框架，涵盖自同构群、模空间分层、不变量、最小模型、雅可比簇等核心内容，并总结了最新进展与开放问题。

函数域上的类域理论与有限阿贝尔 torsors

Class field theory for function fields and finite abelian torsors

本文将经典几何类域理论推广到函数域，通过一般化雅可比簇的同态来分类fppf torsors，并用塞雷-奥尔特基本群描述阿贝尔化诺伊基本群。

Hyperelliptic modular curves $X_0(n)$ and isogenies of elliptic curves over quadratic fields

Let $n$ be an integer such that the modular curve $X_0(n)$ is hyperelliptic of genus $\ge2$ and such that the Jacobian of $X_0(n)$ has rank $0$ over $\mathbb Q$. We determine all points of $X_0(n)$ defined over quadratic fields, and we give a moduli interpretation of these points. As a consequence, we show that up to $\overline{\mathbb Q}$-isomorphism, all but finitely many elliptic curves with $n$-isogenies over quadratic fields are in fact $\mathbb Q$-curves, and we list all exceptions. We also show that, again with finitely many exceptions up to $\overline{\mathbb Q}$-isomorphism, every $\m…

Algorithms to enumerate superspecial Howe curves of genus 4

A Howe curve is a curve of genus $4$ obtained as the fiber product of two genus-$1$ double covers of $\mathbf{P}^1$. In this paper, we present a simple algorithm for testing isomorphism of Howe curves, and we propose two main algorithms for finding and enumerating these curves: One involves solving multivariate systems coming from Cartier--Manin matrices, while the other uses Richelot isogenies of curves of genus $2$. Comparing the two algorithms by implementation and by complexity analyses, we conclude that the latter enumerates curves more efficiently. Using these algorithms, we show that th…

Efficient computation of Cantor's division polynomials of hyperelliptic curves over finite fields

Let $p$ be an odd prime number. We propose an algorithm for computing rational representations of isogenies between Jacobians of hyperelliptic curves via-adic differential equations with a sharp analysis of the loss of precision. Consequently, after having possibly lifted the problem in the $p$-adics, we derive fast algorithms for computing explicitly Cantor's division polynomials of hyperelliptic curves defined over finite fields.