Iwasawa invariants for elliptic curves over ℤ p -extensions and Kida's formula

Abstract

Abstract This paper aims at studying the Iwasawa λ-invariant of the p-primary Selmer group. We study the growth behavior of p-primary Selmer groups in p-power degree extensions over non-cyclotomic ℤ p {\mathbb{Z}_{p}} -extensions of a number field. We prove a generalization of Kida’s formula in such a case. Unlike the cyclotomic ℤ p {\mathbb{Z}_{p}} -extension, where all primes are finitely decomposed, in the ℤ p {\mathbb{Z}_{p}} -extensions we consider primes may be infinitely decomposed. In the second part of this paper, we study the relationship of Iwasawa invariants with respect to congruences, obtaining refinements of the results of Greenberg, Vatsal and Kidwell. As an application, we provide an algorithm for constructing elliptic curves with large anticyclotomic λ-invariant. Our results are illustrated by explicit computation.