On special geometry of the moduli space of string vacua with fluxes
In this paper we construct a special geometry over the moduli space of type II string vacua with both NS and RR fluxes turning on. Depending on what fluxes are turning on we divide into three cases of moduli space of generalized structures. They are respectively generalized Calabi-Yau structures, generalized Calabi-Yau metric structures and ${\cal N} =1$ generalized string vacua. It is found that the $d d^{\cal J}$ lemma can be established for all three cases. With the help of the $d d^{\cal J}$ lemma we identify the moduli space locally as a subspace of $d_{H}$ cohomologies. This leads naturally to the special geometry of the moduli space. It has a flat symplectic structure and a K$\ddot{\rm a}$hler metric with the Hitchin functional (modified if RR fluxes are included) the K$\ddot{\rm a}$hler potential. Our work is based on previous works of Hitchin and recent works of Gra$\tilde{\rm n}$a-Louis-Waldram, Goto, Gualtieri, Yi Li and Tomasiello. The special geometry is useful in flux compactifications of type II string theories.