A new family of elliptic curves with unbounded rank

Abstract

Let ${\mathbb{F}}_q$ be a finite field of odd characteristic and $K={\mathbb{F}}_q(t)$. For any integer $d\ge 2$ coprime to $q$, consider the elliptic curve $E_d$ over $K$ defined by $y^2=x(x^2+t^{2d}x-4t^{2d})$. We show that the rank of the Mordell--Weil group $E_d(K)$ is unbounded as $d$ varies. The curve $E_d$ satisfies the BSD conjecture, so that its rank equals the order of vanishing of its $L$-function at the central point. We provide an explicit expression for the $L$-function of $E_d$, and use it to study this order of vanishing in terms of $d$.

19 pages. Comments very welcome!