A magnetic modular form

Abstract

In this paper, we prove a conjecture of Broadhurst and Zudilin \cite{BZ17} concerning a divisibility property of the Fourier coefficients of a meromorphic modular form using the generalization of the Shimura lift by Borcherds \cite{Borcherds98} and Hecke operators on vector-valued modular forms developed by Bruinier and Stein \cite{BS10}. Furthermore, we construct a family of meromorphic modular forms with this property.

Version 2 contains a new result, Theorem 1.5, and some minor changes