On Shafarevich-Tate groups and analytic ranks in families of modular forms, II. Coleman families

Abstract

This is the second article in a two-part project whose aim is to study algebraic and analytic ranks in $p$-adic families of modular forms. Let $f$ be a newform of weight $2$, square-free level $N$ and trivial character, let $A_f$ be the abelian variety attached to $f$, whose dimension will be denoted by $d_f$, and for every prime number $p\nmid N$ let ${\mathbf{f}}^{(p)}$ be a $p$-adic Coleman family through $f$ over a suitable open disc in the $p$-adic weight space. We prove that, for all but finitely many primes $p$ as above, if $A_f(\mathbb{Q})$ has rank $r\in \{0,d_f\}$ and the $p$-primary part of the Shafarevich-Tate group of $A_f$ over $\mathbb{Q}$ is finite, then all classical specializations of ${\mathbf{f}}^{(p)}$ of weight congruent to $2$ modulo $2(p-1)$ and trivial character have finite $p$-primary Shafarevich-Tate group and $r/d_f$-dimensional image of the relevant $p$-adic étale Abel-Jacobi map. As a second contribution, assuming the non-degeneracy of certain height pairings à la Gillet-Soulé between Heegner cycles, we show that, for all but finitely many $p$, if $f$ has analytic rank $r\in \{0,1\}$, then all classical specializations of ${\mathbf{f}}^{(p)}$ of weight congruent to $2$ modulo $2(p-1)$ and trivial character have analytic rank $r$. This result provides some evidence for a conjecture of Greenberg on analytic ranks in families of modular forms.

arXiv commentSlight revision following the referee's report; 32 pages. Final version, to appear in Mathematical Research Letters