Edited 4-Theta embeddings of Jacobians

Abstract

By the Lefschetz embedding theorem, a principally polarized $g$-dimensional abelian variety is embedded into projective space by the linear system of $4^g$ half-characteristic theta functions. Suppose we {\em edit} this linear system by dropping all the theta functions vanishing at the origin to order greater than parity requires. We prove that for Jacobians the edited $4\Theta$ linear system still defines an embedding into projective space. Moreover, we prove that the projective models of Jacobians arising from the elementary construction of Jacobians recently given by the author are (after passage to linear hulls) copies of the edited $4\Theta$ model. Thus, for all compact Riemann surfaces, we tie together algebraic and analytic Jacobians in a new way.