Divisibility questions in commutative algebraic groups

Abstract

Let $k$ be a number field, let ${\mathcal{A}}$ be a commutative algebraic group defined over $k$ and let $p$ be a prime number. Let ${\mathcal{A}}[p]$ denote the $p$-torsion subgroup of ${\mathcal{A}}$. We give some sufficient conditions for the local-global divisibility by $p$ in ${\mathcal{A}}$ and the triviality of $Sha (k,{\mathcal{A}}[p])$. When ${\mathcal{A}}$ is an abelian variety principally polarized, those conditions imply that the elements of the Tate-Shafarevich group $Sha(k,{\mathcal{A}})$ are divisible by $p$ in the Weil-Ch\^atelet group $H^1(k,{\mathcal{A}})$ and the local-global principle for divisibility by $p$ holds in $H^r(k,{\mathcal{A}})$, for all $r\geq 0$.