On completely faithful Selmer groups of elliptic curves and Hida deformations

Abstract

In this paper, we study completely faithful torsion $\mathbb{Z}_p[[G]]$-modules with applications to the study of Selmer groups. Namely, if $G$ is a nonabelian group belonging to certain classes of polycyclic pro-$p$ group, we establish the abundance of faithful torsion $\mathbb{Z}_p[[G]]$-modules, i.e., non-trivial torsion modules whose global annihilator ideal is zero. We then show that such $\mathbb{Z}_p[[G]]$-modules occur naturally in arithmetic, namely in the form of Selmer groups of elliptic curves and Selmer groups of Hida deformations. It is interesting to note that faithful Selmer groups of Hida deformations do not seem to appear in literature before. We will also show that faithful Selmer groups have various arithmetic properties. Namely, we show that faithfulness is an isogeny invariant, and we prove "control theorem" results on the faithfulness of Selmer groups over a general admissible $p$-adic Lie extension.