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arXiv · 2508.04844

Single-valued periods of meromorphic modular forms and a motivic interpretation of the Gross-Zagier conjecture

Francis Brown·Tiago J. Fonseca
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Abstract

A well-known conjecture of Gross and Zagier states that the values of the higher automorphic Green's function at pairs of points with complex multiplication in the upper half-plane are proportional to the logarithm of an algebraic number. It was recently settled in the case of congruence subgroups of the form $\Gamma_0(N)$ by analytic methods. In this paper we provide a geometric and motivic interpretation of the general conjecture, and show that it is a consequence of a standard conjecture in the theory of motives. In addition, we define a new class of matrix-valued higher Green's functions for both odd and even weight modular forms, and show that they are single-valued periods of a motive constructed from a suitable moduli stack of elliptic curves with marked points. The motive has the structure of a biextension involving symmetric powers of the motives of elliptic curves. This suggests a very general extension of the Gross-Zagier conjecture relating values of matrix-valued higher Green's functions at points which do not necessarily have complex multiplication to special values of $L$-functions. In particular, our motivic interpretation of the Gross-Zagier log-algebraicity conjecture enables us to give a completely geometric proof in level 1 and weight 4 by showing that the motive of the moduli stack $\mathcal{M}_{1,3}$ of elliptic curves with 3 marked points is mixed Tate. In the course of this paper we develop many new foundational results on: the theory of weak harmonic lifts, meromorphic modular forms, biextensions of modular motives, and their corresponding algebraic de Rham cohomology and single-valued periods, which may all be of independent interest.

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BibTeXRIS

Francis Brown, Tiago J. Fonseca. 2025-08-06. Single-valued periods of meromorphic modular forms and a motivic interpretation of the Gross-Zagier conjecture. https://arxiv.org/abs/2508.04844

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