English

On a probabilistic local-global principle for torsion on elliptic curves

Number Theory 2021-07-20 v3

Abstract

Let mm be a positive integer and let EE be an elliptic curve over Q\mathbb{Q} with the property that m\mid#E(\mathbb{F}_p) for a density 11 set of primes pp. Building upon work of Katz and Harron-Snowden, we study the probability that mm divides the the order of the torsion subgroup of E(Q)E(\mathbb{Q}): we find it is nonzero for all m{1,2,,10,12,16}m \in \{ 1, 2, \dots, 10, 12, 16\} and we compute it exactly when m{1,2,3,4,5,7}m \in \{ 1,2,3,4,5,7 \}. As a supplement, we give an asymptotic count of elliptic curves with extra level structure when the parametrizing modular curve arises from the quotient by a torsion-free group of genus zero.

Keywords

Cite

@article{arxiv.2005.06669,
  title  = {On a probabilistic local-global principle for torsion on elliptic curves},
  author = {John Cullinan and Meagan Kenney and John Voight},
  journal= {arXiv preprint arXiv:2005.06669},
  year   = {2021}
}

Comments

51 pages, 2 figures; incorporated final corrections and added/updated references