$p^r$-Selmer companion modular forms

TL;DR

This paper extends the concept of Selmer companions from elliptic curves to modular forms, comparing various Selmer groups and exploring their relations with congruences and special values of L-functions.

Contribution

It introduces an analogue of $p^r$-Selmer companions for modular forms and analyzes their properties in relation to Bloch-Kato, Greenberg, and signed Selmer groups.

Findings

Established conditions for Selmer group isomorphisms in modular forms.

Compared Bloch-Kato Selmer groups with Greenberg and signed Selmer groups.

Connected Selmer group congruences with special L-value results.

Abstract

The study of $n$-Selmer group of elliptic curve over number field in recent past has led to the discovery of some deep results in the arithmetic of elliptic curves. Given two elliptic curves $E_1$ and $E_2$ over a number field $K$, Mazur-Rubin\cite{mr} have defined them to be {\it $n$-Selmer companion} if for every quadratic twist $\chi$ of $K$, the $n$-Selmer groups of $E_1^\chi $ and $E_2^\chi$ over $K$ are isomorphic. Given a prime $p$, they have given sufficient conditions for two elliptic curves to be $p^r$-Selmer companion in terms of mod-$p^r$ congruences between the curves. We discuss an analogue of this for Bloch-Kato $p^r$-Selmer group of modular forms. We compare the Bloch-Kato Selmer groups of a modular form respectively with the Greenberg Selmer group when the modular form is $p$-ordinary and with the signed Selmer group of Lei-Loeffler-Zerbes when the modular form is non-ordinary at $p$. We also indicate the corresponding results over $\Q_\cyc$ and its relation with the well known congruence results of the special values of the corresponding $L$-functions due to Vatsal.