Impossible intersections in a Weierstrass family of elliptic curves

Niki Myrto Mavraki

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Consider the Weierstrass family of elliptic curves Eλ:y2=x3 parametrized by nonzero λ∈Q2, and let Pλ(x)=(x,x3+λ)∈Eλ. In this article, given α,β∈Q2 such that αβ∈Q, we provide an explicit description for the set of parameters λ such that Pλ(α) and Pλ(β) are simultaneously torsion for Eλ. In particular we prove that the aforementioned set is empty unless αβ∈{−2,−12}. Furthermore, we show that this set is empty even when αβ∉Q provided that α and β have distinct 2-adic absolute values and the ramification index e(Q2(αβ)|Q2) is coprime with 6. We also improve upon a recent result of Stoll concerning the Legendre family of elliptic curves Eλ:y2=x(x−1)(x−λ), which itself strengthened earlier work of Masser and Zannier by establishing that provided a,b have distinct reduction modulo 2, the set {λ∈C∖{0,1}:(a,a(a−1)(a−λ)),(b,b(b−1)(b−λ))∈(Eλ)tors} is empty.

Original languageEnglish (US)
Pages (from-to)21-40
Number of pages20
JournalJournal of Number Theory
StatePublished - Dec 1 2016


  • Attracting fixed point
  • Elliptic curve
  • Family of Lattès maps
  • Impossible intersections
  • Preperiodic point
  • Torsion

ASJC Scopus subject areas

  • Algebra and Number Theory

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