On an Algorithm for Computing Degrees of Parametrizations of Elliptic Curves by Shimura Curves

Alyson Deines

Let E be an elliptic curve over with square-free conductor N and let f S2(N) be the associated modular form. Then via Jaquet-Langlands there is exists f′∈ S2D(M), where B is the quaternion algebra over of discriminant D, N = DM, and S2D(M) represents the quaternionic modular forms on B of level M. Takahashi shows that there is an elliptic curve E, isogenous to E such that Eis parameterized by the Jacobian of the Shimura curve X0D(M). Note that if D = 1 then this is just the modular curve case where X0D(N) = X0(N). I outline an algorithm which computes the degree of this parametrization and the isogenous curve Eand look at ways to expand this result to abelian varieties and elliptic curves over number fields.