The non-$p$-part of the fine Selmer group in a $\mathbb Z_p$-extension
Volume 213 / 2024
Abstract
Fix two distinct primes $p$ and $\ell $. Let $A$ be an abelian variety over $\mathbb Q(\zeta _{\ell })$, the cyclotomic field of $\ell $th roots of unity. Suppose that $A(\mathbb Q (\zeta _{\ell }))[\ell ] \neq 0$. We show that there exists a number field $L$ and a $\mathbb Z_p$-extension $L_{\infty }/L$ where the $\ell $-primary fine Selmer group of $A$ grows arbitrarily quickly. This is a fine Selmer group analogue of a theorem of Washington that there are certain (non-cyclotomic) $\mathbb Z_p$-extensions where the $\ell $-part of the class group can grow arbitrarily quickly. We also prove this for a wide class of non-commutative $p$-adic Lie extensions. Finally, we include several examples to illustrate this theorem.