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Power residues of Fourier coefficients of modular forms
CANADIAN JOURNAL OF MATHEMATICS-JOURNAL CANADIEN DE MATHEMATIQUES
  • T Weston, University of Massachusetts - Amherst
Publication Date
2005
Abstract
Let ρ:G\Q→\GLn(\Ql) be a motivic ℓ-adic Galois representation. For fixed m>1 we initiate an investigation of the density of the set of primes p such that the trace of the image of an arithmetic Frobenius at p under ρ is an m-th power residue modulo p. Based on numerical investigations with modular forms we conjecture (with Ramakrishna) that this density equals 1/m whenever the image of ρ is open. We further conjecture that for such ρ the set of these primes p is independent of any set defined by Cebatorev-style Galois-theoretic conditions (in an appropriate sense). We then compute these densities for certain m in the complementary case of modular forms of CM-type with rational Fourier coefficients; our proofs are a combination of the Cebatorev density theorem (which does apply in the CM case) and reciprocity laws applied to Hecke characters. We also discuss a potential application (suggested by Ramakrishna) to computing inertial degrees at p in abelian extensions of imaginary quadratic fields unramified away from p.
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The published version is located at http://www.math.ca/10.4153/CJM-2005-042-5

Pages
1102-1120
Citation Information
T Weston. "Power residues of Fourier coefficients of modular forms" CANADIAN JOURNAL OF MATHEMATICS-JOURNAL CANADIEN DE MATHEMATIQUES Vol. 57 Iss. 5 (2005)
Available at: http://works.bepress.com/tom_weston/7/