Definite orthogonal modular forms: Computations, Excursions and Discoveries

Eran Assaf, Dan Fretwell, Colin Ingalls, Adam Logan, Spencer Secord, John Voight

    Research output: Working paperPreprint

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    Abstract

    We consider spaces of modular forms attached to definite orthogonal groups of low even rank and nontrivial level, equipped with Hecke operators defined by Kneser neighbours. After reviewing algorithms to compute with these spaces, we investigate endoscopy using theta series and a theorem of Rallis. Along the way, we exhibit many examples and pose several conjectures. As a first application, we express counts of Kneser neighbours in terms of coefficients of classical or Siegel modular forms, complementing work of Chenevier-Lannes. As a second application, we prove new instances of Eisenstein congruences of Ramanujan and Kurokawa-Mizumoto type.
    Original languageEnglish
    PublisherarXiv
    Number of pages31
    DOIs
    Publication statusPublished - 12 Mar 2022

    Keywords

    • math.NT

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