New unlikely intersections on elliptic surfaces

TL;DR

This paper extends previous results on unlikely intersections in elliptic surfaces from complex numbers to positive characteristic, introduces new methods, and clarifies the role of a key homomorphism of Manin.

Contribution

It generalizes bounds on tangencies to positive characteristic and develops a novel approach linking unlikely intersections to Manin's homomorphism.

Findings

Extended unlikely intersection bounds to characteristic p

Developed a new approach to algebraic curve tangencies

Clarified the role of Manin's homomorphism in elliptic surfaces

Abstract

Consider a Jacobian elliptic surface $E \to C$ with a section $P$ of infinite order. Previous work of the first author and Urz\'ua over the complex numbers gives a bound on the number of tangencies between $P$ and a torsion section of $E$ (an ``unlikely intersection''), and more precisely, an exact formula for the weighted number of tangencies between $P$ and elements of the ``Betti foliation''. This work used analytic techniques that apparently do not generalize to positive characteristic. In this paper, we extend their work to characteristic $p$, and we develop a second approach to tangency properties of algebraic curves on a complex elliptic surface, yielding a new family of unlikely intersections with a strong connection to a famous homomorphism of Manin. We also correct inaccuracies in the literature about this homomorphism.