English

Class group statistics for torsion fields generated by elliptic curves

Number Theory 2025-03-26 v2

Abstract

For a prime pp and a rational elliptic curve E/QE_{/\mathbb{Q}}, set K=Q(E[p])K=\mathbb{Q}(E[p]) to denote the torsion field generated by E[p]:=ker{EpE}E[p]:=\operatorname{ker}\{E\xrightarrow{p} E\}. The class group ClK\operatorname{Cl}_K is a module over Gal(K/Q)\operatorname{Gal}(K/\mathbb{Q}). Given a fixed odd prime number pp, we study the average non-vanishing of certain Galois stable quotients of the mod-pp class group ClK/pClK\operatorname{Cl}_K/p\operatorname{Cl}_K. Here, EE varies over rational elliptic curves, ordered according to \emph{height}. Our results are conditional and rely on predictions made by Delaunay and Poonen-Rains for the statistical variation of the pp-primary parts of Tate-Shafarevich groups of elliptic curves. We also prove results in the case when the elliptic curve E/QE_{/\mathbb{Q}} is fixed and the prime pp is allowed to vary.

Keywords

Cite

@article{arxiv.2204.09757,
  title  = {Class group statistics for torsion fields generated by elliptic curves},
  author = {Anwesh Ray and Tom Weston},
  journal= {arXiv preprint arXiv:2204.09757},
  year   = {2025}
}

Comments

Version 2: Minor corrections and expository improvements to the introduction. Paper accepted for publication in the Journal of the Australian Math Soc

R2 v1 2026-06-24T10:53:58.312Z