Algebraic CM-supported residues of magnetic modular forms

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Let ff be a magnetic modular form of weight kk. For each integer mm with 0≤m≤k−20\leq m\leq k-2, consider the residues of τmf(τ)\tau^m f(\tau) at the relevant points. A point in the upper half-plane is a complex multiplication point if it corresponds to a CM elliptic curve.

Residue conjecture. The residues of τmf(τ)\tau^m f(\tau) satisfy

Res⁡(τmf(τ))∈1(2πi)k/2Q‾,\operatorname{Res}\bigl(\tau^m f(\tau)\bigr)\in \frac{1}{(2\pi i)^{k/2}}\overline{\mathbb{Q}},

and they are nonzero only at complex multiplication points.

The conjecture is based on computations of residues for many examples and candidates. It predicts both an algebraicity statement and a strong restriction on the locations where residues can occur.

References

Primary source

Kilian Bönisch, Claude Duhr and Sara Maggio, “Some conjectures around magnetic modular forms”, arXiv:2404.04085 (2024).

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