Congruence-ideal conjecture for non-base-change Hilbert cuspforms

Let ff be a normalized newform and fFf_F its base change to FF. Let ηf\eta_f^\sharp be the complementary factor in the factorization of the base-change congruence ideal, let IGI_G denote the relevant character associated with the extension, and let IrrF\operatorname{Irr}_F be the irreducibility hypothesis. Assume that pp does not divide 6dDNϕF(N)6dDN\phi_F(N), (IrrF)(\operatorname{Irr}_F) holds, and the Hecke algebras T\mathcal{T} and TF\mathcal{T}_F are Gorenstein. Congruence-ideal conjecture. One has

ηfL(AdfIG).\eta_f^\sharp\sim L^\ast(\operatorname{Ad} f\otimes I_G).

In particular, if pp divides L(AdfIG)L^\ast(\operatorname{Ad} f\otimes I_G), the source predicts a congruence between fFf_F and a non-base-change Hilbert cuspform. The source says this will be proved in the real quadratic case; no general resolution is supplied.

Sources & referencesView supporting material

Primary source

Jacques Tilouine and Eric Urban, “Integral period relations and congruences”, arXiv:1811.11166 (2021).

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