## Abstract

We look at genera of even unimodular lattices of rank 12 over the ring of integers of Q(5) and of rank 8 over the ring of integers of Q(3), using Kneser neighbours to diagonalise spaces of scalar-valued algebraic modular forms. We conjecture most of the global Arthur parameters, and prove several of them using theta series, in the manner of Ikeda and Yamana. We find instances of congruences for non-parallel weight Hilbert modular forms. Turning to the genus of Hermitian lattices of rank 12 over the Eisenstein integers, even and unimodular over Z, we prove a conjecture of Hentschel, Krieg and Nebe, identifying a certain linear combination of theta series as an Hermitian Ikeda lift, and we prove that another is an Hermitian Miyawaki lift.

Original language | English |
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Pages (from-to) | 29-67 |

Number of pages | 39 |

Journal | Abhandlungen aus dem Mathematischen Seminar der Universitat Hamburg |

Volume | 91 |

Issue number | 1 |

Early online date | 20 Feb 2021 |

DOIs | |

Publication status | Published - Apr 2021 |

Externally published | Yes |

## Keywords

- Algebraic modular forms
- Even unimodular lattices
- Hermitian modular forms
- Hilbert modular forms
- Theta series