Comments on T-Dualities of Ramond-Ramond Potentials

The type IIA/IIB effective actions compactified on T^d are known to beinvariant under the T-duality group SO(d, d; Z) although the invariance of theR-R sector is not so direct to see. Inspired by a work of Brace, Morariu andZumino,we introduce new potentials which are mixture of R-R potentials and theNS-NS 2-form in order to make the invariant structure of R-R sector moretransparent. We give a simple proof that if these new potentials transform as aMajorana-Weyl spinor of SO(d, d; Z), the effective actions are indeed invariantunder the T-duality group. The argument is made in such a way that it can applyto Kaluza-Klein forms of arbitrary degree. We also demonstrate that these newfields simplify all the expressions including the Chern-Simons term.Comment: 26 pages; LaTeX; major version up; discussion on the Chern-Simons term added; references adde