Picard Groups of Siegel Modular 3-Folds and θ-Liftings
Journal of Lie Theory, Volume 22 (2012) no. 3, pp. 769-801
\def\R{{\Bbb R}} We show that the Humbert surfaces rationally generate the Picard groups of Siegel modular threefolds. This involves three ingredients: (1) R. Weissauer's determination of these Picard groups in terms of theta lifting from cusp forms of weight $5/2$ on $\tilde{\rm SL}_2(\R)$ to automorphic forms on ${\rm Sp}_4(\R)$. (2) The theory of special cycles due to Kudla/Millson and Tong/Wang relating cohomology defined by automorphic forms to that defined by certain geometric cycles. (3) Results of R. Howe about the structure of the oscillator representation in this situation.
DOI: 10.5802/jolt.691
Classification: 14G35, 11F46, 11F27, 14C22, 11F23
Keywords: Siegel modular threefold, Picard group, theta lifting
@article{JOLT_2012_22_3_a7,
     author = {H. He and J. W. Hoffman},
     title = {Picard {Groups} of {Siegel} {Modular} {3-Folds} and {\ensuremath{\theta}-Liftings}},
     journal = {Journal of Lie Theory},
     pages = {769--801},
     year = {2012},
     volume = {22},
     number = {3},
     doi = {10.5802/jolt.691},
     zbl = {1252.14018},
     url = {https://jolt.centre-mersenne.org/articles/10.5802/jolt.691/}
}
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H. He; J. W. Hoffman. Picard Groups of Siegel Modular 3-Folds and θ-Liftings. Journal of Lie Theory, Volume 22 (2012) no. 3, pp. 769-801. doi: 10.5802/jolt.691

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