Rational Points of Bounded Height on Genus Zero Moular Curves and Average Analytic Ranks of Elliptic Curves over Number Fields

Tristan Phillips

Published 2022-01-25Version 1

We give asymptotics for the number of isomorphism classes of elliptic curves over arbitrary number fields with certain prescribed level structures and prescribed local conditions. In particular, we count the number of points of bounded height on genus zero modular curves which are isomorphic to either a weighted projective space or $\mathbb{P}^1\times\mathbb{P}(2)$. This includes the cases of $\mathcal{X}(N)$ for $N\in\{1,2,3,4,5\}$, $\mathcal{X}_1(N)$ for $N\in\{1,2,\dots,10,12\}$, and $\mathcal{X}_0(N)$ for $N\in\{4,6,8,9,12,16,18\}$. In all cases we give an asymptotic with an expression for the leading coefficient. Our results for counting points on modular curves follow from more general results for counting points of bounded height on weighted projective spaces. Using our results for counting elliptic curves over number fields with a prescribed local condition, we are able to give a conditional bound for the average analytic rank of elliptic curves over an arbitrary number field. In particular, under the assumptions that all elliptic curves over a number field $K$ are modular and have $L$-functions which satisfy the Generalized Riemann Hypothesis, we show that the average analytic rank of isomorphism classes of elliptic curves over $K$ is bounded above by $3\text{deg}(K)+1/2$.