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arXiv · 1110.6430

Hecke Eigenforms as Products of Eigenforms

Matthew L. Johnson
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Abstract

We investigate when the product of two Hecke eigenforms for Γ_1(N) is again a Hecke eigenform. In this paper we prove that the product of two normalized eigenforms for Γ_1(N), of weight greater than 1, is an eigenform only 61 times, and give a complete list. Duke [Duk99] and Ghate [Gha00] independently proved that with eigenforms for SL_2(Z), there are only 16 such product identities. Ghate [Gha02] also proved related results for Γ_1(N), with N square free. Emmons [Emm05] proved results for eigenforms away from the level, for prime level. The methods we use are elementary and effective, and do not rely on the Rankin-Selberg convolution method used by both Duke and Ghate.

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Matthew L. Johnson. 2011-10-28. Hecke Eigenforms as Products of Eigenforms. https://arxiv.org/abs/1110.6430

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