Proving Modularity for a given elliptic curve over an imaginary quadratic field

Abstract

We present an algorithm to determine if the L-series associated to an automorphic representation and the one associated to an elliptic curve over an imaginary quadratic field agree. By the work of Harris-Soudry-Taylor, Taylor and Berger-Harcos (cf. [HST93], [Tay94] and [BH07]) we can associate to an automorphic representation a family of compatible ℓ-adic representations. Our algorithm is based on Faltings-Serre’s method to prove that ℓ-adic Galois representations are isomorphic. Using the algorithm we provide the first examples of modular elliptic curves over imaginary quadratic fields with residual 2-adic image isomorphic to S3 and C3.