# Genuine Bianchi modular forms of higher level, at varying weight and discriminant

## TL;DR

This paper extends the understanding of Bianchi modular forms by developing formulas for non-genuine forms at higher levels and identifying rare genuine forms at increased levels and weights, advancing the theory related to imaginary quadratic fields.

## Contribution

It introduces formulas for non-genuine Bianchi modular forms at deeper levels and reports the first instances of genuine forms at higher levels and weights.

## Key findings

- Extended formulas for non-genuine forms to deeper levels.
- Identified rare genuine forms at higher levels and weights.
- Contributed to the extension of the modularity theorem for imaginary quadratic fields.

## Abstract

Bianchi modular forms are automorphic forms over an imaginary quadratic field, associated to a Bianchi group. Even though modern studies of Bianchi modular forms go back to the mid 1960's, most of the fundamental problems surrounding their theory are still wide open. Only for certain types of Bianchi modular forms, which we will call non-genuine, it is possible at present to develop dimension formulas: They are (twists of) those forms which arise from elliptic cuspidal modular forms via the Langlands Base-Change procedure, or arise from a quadratic extension of the imaginary quadratic field via automorphic induction (so-called CM-forms). The remaining Bianchi modular forms are what we call genuine, and they are of interest for an extension of the modularity theorem (formerly the Taniyama-Shimura conjecture, crucial in the proof of Femat's Last Theorem) to imaginary quadratic fields. In a preceding paper by Rahm and Sengun, an extreme paucity of genuine cuspidal Bianchi modular forms has been reported, but those and other computations were restricted to level One. In this paper, we are extending the formulas for the non-genuine Bianchi modular forms to deeper levels, and we are able to spot the first, rare instances of genuine forms at deeper level and heavier weight.