Unlikely intersections on the $p$-adic formal ball

TL;DR

This paper explores $p$-adic formal intersections related to the Mordell--Lang conjecture, establishing bounds on torsion points in formal groups, providing counterexamples, and discussing implications for automorphic forms in $p$-adic deformations.

Contribution

It generalizes $p$-adic Manin--Mumford results to higher dimensions, proves uniform bounds for torsion points, and presents counterexamples to a full $p$-adic Mordell--Lang conjecture.

Findings

Uniform bounds on torsion points under certain conditions

Counterexamples to the full $p$-adic formal Mordell--Lang conjecture

Implications for the density of automorphic forms in $p$-adic families

Abstract

We investigate generalizations along the lines of the Mordell--Lang conjecture of the author's $p$-adic formal Manin--Mumford results for $n$-dimensional $p$-divisible formal groups $\mathcal{F}$. In particular, given a finitely generated subgroup $\Gamma$ of $\mathcal{F}(\overline{\mathbb{Q}}_p)$ and a closed subscheme $X\hookrightarrow \mathcal{F}$, we show under suitable assumptions that for any points $P\in X(\mathbb{C}_p)$ satisfying $nP\in\Gamma$ for some $n\in\mathbb{N}$, the minimal such orders $n$ are uniformly bounded whenever $X$ does not contain a formal subgroup translate of positive dimension. In contrast, we then provide counter-examples to a full $p$-adic formal Mordell--Lang result. Finally, we outline some consequences for the study of the Zariski-density of sets of automorphic objects in $p$-adic deformations. Specifically, we do so in the context of the nearly ordinary $p$-adic families of cuspidal cohomological automorphic forms for the general linear group constructed by Hida.