  We use Young's raising operators to introduce and study double theta
polynomials, which specialize to both the theta polynomials of Buch, Kresch,
and Tamvakis, and to double (or factorial) Schur S-polynomials and
Q-polynomials. These double theta polynomials give Giambelli formulas which
represent the equivariant Schubert classes in the torus-equivariant cohomology
ring of symplectic Grassmannians, and we employ them to obtain a new
presentation of this ring in terms of intrinsic generators and relations.
