Siegel modular forms of genus 2 attached to elliptic curves

The object of this article is to construct certain classes of arithmetically significant, holomorphic Siegel cusp forms F of genus 2, which are neither of Saito-Kurokawa type, in which case the degree 4 spinor L-function L(s, F) is divisible by an abelian L-function, nor of Yoshida type, in which case L(s,F) is a product of L-series of a pair of elliptic cusp forms. Two key examples are the forms F defined by the symmetric cube of a non-CM elliptic curve E over the rationals, and those defined by anticyclotomic twists (of even non-zero weight) of the base change of such an E to an imaginary quadratic field K. One of the main ingredients is the transfer, albeit indirect, of cusp forms \pi on GL(4) to GSp(4) with many of the expected properties, and this might be of independent interest. The transfer information is shown to be complete when \pi is regular and associated to an \ell-adic Galois representation. We also appeal to the (independent) results of Laumon and Weissauer on the zeta functions of Siegel modular threefolds.