Quantitative level lowering for weight two Hilbert modular forms

Abstract

We generalize a result of Ribet and Takahashi on the parametrization of elliptic curves by Shimura curves to the Hilbert modular setting. In particular, we study the behaviour of the parametrization of modular abelian varieties by Shimura curves associated to quaternion algebras $D$ over a totally real field $F$, as we vary $D$. As a consequence, we obtain that on these Shimura curves, the cohomological congruence module is equal to the ring theoretic congruence module even in cases where we do not have multiplicity one, thereby extending results of Manning and Böckle-Khare-Manning.

Accepted version. Exposition substantially improved in response to referee comments; added an appendix and an example illustrating the main theorem