Primitive divisors of sequences associated to elliptic curves over function fields

Robert Slob

Published 2021-03-11Version 1

We study the existence of a Zsigmondy bound for a sequence of divisors associated to points on an elliptic curve over a function field. More precisely, let $k$ be an algebraically closed field, let $\mathcal{C}$ be a nonsingular projective curve over $k$, and let $K$ denote the function field of $\mathcal{C}$. Suppose $E$ is an ordinary elliptic curve over $K$ and suppose there does not exist an elliptic curve $E_0$ defined over $k$ that is isomorphic to $E$ over $K$. Suppose $P\in E(K)$ is a non-torsion point and $Q\in E(K)$ is a torsion point of prime order $r$. The sequence of points $\{nP+Q\}\subset E(K)$ induces a sequence of effective divisors $\{D_{nP+Q}\}$ on $\mathcal{C}$. We provide conditions on $r$ and the characteristic of $k$ for there to exist a bound $N$ such that $D_{nP+Q}$ has a primitive divisor for all $n\geq N$. This extends the analogous result of Verzobio in the case where $K$ is a number field.