Fields of rationality of cusp forms
Author(s)
Binder, John
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Abstract
In this paper, we prove that for any totally real field F, weight k, and nebentypus character χ, the proportion of Hilbert cusp forms over F of weight k and character χ with bounded field of rationality approaches zero as the level grows large. This answers, in the affirmative, a question of Serre. The proof has three main inputs: first, a lower bound on fields of rationality for admissible GL2 representations; second, an explicit computation of the (fixed-central-character) Plancherel measure for GL2; and third, a Plancherel equidistribution theorem for cusp forms with fixed central character. The equidistribution theorem is the key intermediate result and builds on earlier work of Shin and Shin–Templier and mirrors work of Finis–Lapid–Mueller by introducing an explicit bound for certain families of orbital integrals.
Date issued
2017-11Department
Massachusetts Institute of Technology. Department of MathematicsJournal
Israel Journal of Mathematics
Publisher
The Hebrew University Magnes Press
Citation
Binder, John. “Fields of Rationality of Cusp Forms.” Israel Journal of Mathematics 222, no. 2 (October 2017): 973–1028. doi:10.1007/s11856-017-1610-z.
Version: Author's final manuscript
ISSN
0021-2172
1565-8511