English

Division of primitive Points in an abelian Variety

Number Theory 2022-07-04 v1 Algebraic Geometry

Abstract

Let AA be an abelian variety defined over a number field KK. We say that a point PA(Q)P \in A(\overline{\mathbb{Q}}) is primitive if there is no QA(Q)Q \in A(\overline{\mathbb{Q}}) defined on the field of definition of PP over KK such that [N]Q=P[N]Q=P for some positive integer N2N \ge 2. For any primitive point PA(Q)P \in A(\overline{\mathbb{Q}}), positive integer NN and point QA(Q)Q \in A(\overline{\mathbb{Q}}) such that [N]Q=P[N]Q=P, we prove an effective lower bound on the degree of the field of definition of QQ over KK of the form NδN^{\delta} that depends only on A,KA,K and the degree of the field of definition of PP over KK. The proof is based on the estimates of the degree of torsion points by Masser. We combine this result with a uniform version of Manin-Mumford to prove an effective Unlikely Intersections-type result: if PA(Q)P \in A(\overline{\mathbb{Q}}) is primitive, defined over a field of degree dd over KK, and XX is a subvariety of AA, then X[N]1PX \cap [N]^{-1}P is contained in the weakly special part of XX, provided NN is bigger than a suitable power of dd. As an application, we study an inverse elliptic Fermat equation, analogous to a modular Fermat equation treated by Pila.

Keywords

Cite

@article{arxiv.2207.00049,
  title  = {Division of primitive Points in an abelian Variety},
  author = {Francesco Ballini},
  journal= {arXiv preprint arXiv:2207.00049},
  year   = {2022}
}

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8 pages