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arXiv · 2602.16248

Intersections of special cycles on Shimura curves and Siegel Maass forms

Jan Hendrik Bruinier·Yingkun Li·Martin Möller
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Abstract

We show that the generating series of the number of pairs of geodesics on a compact Shimura curve with given discriminants and intersection angle are coefficients of a non-holomorphic Siegel modular form, a theta lift of the constant function. This retrieves and generalizes counting results of Rickards via the Siegel-Weil formula. More generally, we study the genus two theta lift of Maass forms on this Shimura curve and prove a Fourier-Taylor expansion in terms of some generalized Whittaker functions. We also provide a geometric interpretation of all Fourier coefficients of these theta lifts in terms of averages of geodesic Taylor coefficients over special cycles.

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Jan Hendrik Bruinier, Yingkun Li, Martin Möller. 2026-02-18. Intersections of special cycles on Shimura curves and Siegel Maass forms. https://arxiv.org/abs/2602.16248

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