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Relations among Ramanujan-type congruences II: Ramanujan-type congruences in half-integral weights

  • Martin Raum ORCID logo EMAIL logo
Veröffentlicht/Copyright: 31. März 2023

Abstract

We link Ramanujan-type congruences, which emerge abundantly in combinatorics, to the Galois- and geometric theory of modular forms. Specifically, we show that Ramanujan-type congruences are preserved by the action of the shallow Hecke algebra, and discover a dichotomy between congruences originating in Hecke eigenvalues and congruences on arithmetic progressions with cube-free periods. The latter provide congruences among algebraic parts of twisted central L -values. We specialize our results to integer partitions, for which we investigate the landmark proofs of partition congruences by Atkin and by Ono. Based on a modulo analogue of the Maeda conjecture for certain partition generating functions, we conclude that their approach by Hecke operators acting diagonally modulo on modular forms is indeed close to optimal. This work is enabled by several structure results for Ramanujan-type congruences that we establish. In an extended example, we showcase how to employ them to also benefit experimental work.

MSC 2020: 11F33; 11F30; 11F67

Communicated by Jan Bruinier


Funding source: Vetenskapsrådet

Award Identifier / Grant number: 2015-04139

Award Identifier / Grant number: 2019-03551

Funding statement: The author was partially supported by Vetenskapsrådet Grants 2015-04139 and 2019-03551.

Acknowledgements

The author wishes to thank Scott Ahlgren, Olivia Beckwith, and Olav Richter for inspiring discussions and helpful comments. The author is also grateful to the referee for their helpful and exceptionally thorough report.

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Received: 2022-02-02
Revised: 2022-09-29
Published Online: 2023-03-31
Published in Print: 2023-05-01

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