English

Primitive divisors of sequences associated to elliptic curves over function fields

Number Theory 2021-03-24 v2 Algebraic Geometry

Abstract

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 kk be an algebraically closed field, let C\mathcal{C} be a nonsingular projective curve over kk, and let KK denote the function field of C\mathcal{C}. Suppose EE is an ordinary elliptic curve over KK and suppose there does not exist an elliptic curve E0E_0 defined over kk that is isomorphic to EE over KK. Suppose PE(K)P\in E(K) is a non-torsion point and QE(K)Q\in E(K) is a torsion point of order rr. The sequence of points {nP+Q}E(K)\{nP+Q\}\subset E(K) induces a sequence of effective divisors {DnP+Q}\{D_{nP+Q}\} on C\mathcal{C}. We provide conditions on rr and the characteristic of kk for there to exist a bound NN such that DnP+QD_{nP+Q} has a primitive divisor for all nNn\geq N. This extends the analogous result of Verzobio in the case where KK is a number field.

Keywords

Cite

@article{arxiv.2103.06787,
  title  = {Primitive divisors of sequences associated to elliptic curves over function fields},
  author = {Robert Slob},
  journal= {arXiv preprint arXiv:2103.06787},
  year   = {2021}
}

Comments

13 pages. New version: in the old version, we assumed in Theorem 1 that the torsion point $Q$ had prime order unequal to the characteristic of $k$. It was pointed out by a colleague that some small adaptations allow us to extend the main theorem to where $Q$ is a torsion point of arbitrary order (as long as the characteristic of $k$ and the order of $Q$ are not too small, see Table 1)

R2 v1 2026-06-24T00:00:37.476Z