English

An elliptic surface with infinitely many fibers for which the rank does not jump

Number Theory 2025-02-04 v1

Abstract

Let EE be a nonisotrivial elliptic curve over Q(T)\mathbb{Q}(T) and denote the rank of the abelian group E(Q(T))E(\mathbb{Q}(T)) by rr. For all but finitely many tQt\in \mathbb{Q}, specialization will give an elliptic curve EtE_t over Q\mathbb{Q} for which the abelian group Et(Q)E_t(\mathbb{Q}) has rank at least rr. Conjecturally, the set of tQt\in\mathbb{Q} for which Et(Q)E_t(\mathbb{Q}) has rank exactly rr has positive density. We produce the first known example for which Et(Q)E_t(\mathbb{Q}) has rank rr for infinitely many tQt\in\mathbb{Q}. For our particular E/Q(T)E/\mathbb{Q}(T) which has rank 00, we will make use of a theorem of Green on 33-term arithmetic progressions in the primes to produce tQt\in\mathbb{Q} for which EtE_t has only a few bad primes that we understand well enough to perform a 22-descent.

Keywords

Cite

@article{arxiv.2502.01026,
  title  = {An elliptic surface with infinitely many fibers for which the rank does not jump},
  author = {David Zywina},
  journal= {arXiv preprint arXiv:2502.01026},
  year   = {2025}
}