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Large families of elliptic curves ordered by conductor

Published online by Cambridge University Press:  22 June 2021

Ananth N. Shankar
Affiliation:
Department of Mathematics, University of Wisconsin-Madison, Madison, WI53706, [email protected]
Arul Shankar
Affiliation:
Department of Mathematics, University of Toronto, Toronto, ONM5S 2E4, [email protected]
Xiaoheng Wang
Affiliation:
Department of Pure Mathematics, University of Waterloo, Waterloo, ONN2L 3G1, [email protected]

Abstract

In this paper we study the family of elliptic curves $E/{{\mathbb {Q}}}$, having good reduction at $2$ and $3$, and whose $j$-invariants are small. Within this set of elliptic curves, we consider the following two subfamilies: first, the set of elliptic curves $E$ such that the quotient $\Delta (E)/C(E)$ of the discriminant divided by the conductor is squarefree; and second, the set of elliptic curves $E$ such that the Szpiro quotient$\beta _E:=\log |\Delta (E)|/\log (C(E))$ is less than $7/4$. Both these families are conjectured to contain a positive proportion of elliptic curves, when ordered by conductor. Our main results determine asymptotics for both these families, when ordered by conductor. Moreover, we prove that the average size of the $2$-Selmer groups of elliptic curves in the first family, again when these curves are ordered by their conductors, is $3$. The key new ingredients necessary for the proofs are ‘uniformity estimates’, namely upper bounds on the number of elliptic curves with bounded height, whose discriminants are divisible by high powers of primes.

Type
Research Article
Copyright
© The Author(s) 2021

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