Computing torsion points on curves.
Constructions of plane curves with many points
Courbes algébriques de genre ≥ 2 possédant de nombreux points rationnels
Covering collections and a challenge problem of Serre
Curves of genus 2, continued fractions, and Somos sequences.
Descent via (3,3)-isogeny on Jacobians of genus 2 curves
We give a parametrization of curves C of genus 2 with a maximal isotropic (ℤ/3)² in J[3], where J is the Jacobian variety of C, and develop the theory required to perform descent via (3,3)-isogeny. We apply this to several examples, where it is shown that non-reducible Jacobians have non-trivial 3-part of the Tate-Shafarevich group.
Dessins d'enfants: bipartite maps and Galois groups.
Errata-Corrige : “The Mordell conjecture revisited”
Estimation effective des points entiers d'une famille de courbes algébriques
Explicit descent for Jacobians of cyclic coevers of the projective line.
Explicit moduli for curves of genus 2 with real multiplication by ℚ(√5)
1. Motivation. Let J₀(N) denote the Jacobian of the modular curve X₀(N) parametrizing pairs of N-isogenous elliptic curves. The simple factors of J₀(N) have real multiplication, that is to say that the endomorphism ring of a simple factor A contains an order in a totally real number field of degree dim A. We shall sometimes abbreviate "real multiplication" to "RM" and say that A has maximal RM by the totally real field F if A has an action of the full ring of integers of F. We say that a...
Explicit Selmer groups for cyclic covers of ℙ¹
For any abelian variety J over a global field k and an isogeny ϕ: J → J, the Selmer group is a subgroup of the Galois cohomology group , defined in terms of local data. When J is the Jacobian of a cyclic cover of ℙ¹ of prime degree p, the Selmer group has a quotient by a subgroup of order at most p that is isomorphic to the ‘fake Selmer group’, whose definition is more amenable to explicit computations. In this paper we define in the same setting the ‘explicit Selmer group’, which is isomorphic...
Familles de revêtements de la droite projective
Fibrations of low genus, I
Galois actions on Néron models of Jacobians
Let be a smooth curve defined over the fraction field of a complete discrete valuation ring . We study a natural filtration of the special fiber of the Néron model of the Jacobian of by closed, unipotent subgroup schemes. We show that the jumps in this filtration only depend on the fiber type of the special fiber of the minimal regular model with strict normal crossings for over , and in particular are independent of the residue characteristic. Furthermore, we obtain information about...
Galois theory and torsion points on curves
In this paper, we survey some Galois-theoretic techniques for studying torsion points on curves. In particular, we give new proofs of some results of A. Tamagawa and the present authors for studying torsion points on curves with “ordinary good” or “ordinary semistable” reduction at a given prime. We also give new proofs of : (1) the Manin-Mumford conjecture : there are only finitely many torsion points lying on a curve of genus at least embedded in its jacobian by an Albanese map; and (2) the...
Generators and equations for modular function fields of principal congruence subgroups
Groupe des points de Weierstrass sur une famille de quartiques lisses
Hyperelliptic modular curves
Hyperelliptic modular curves X₀*(N) with square-free levels