principle by an exact computation of the periods, which was done for the model at hand in [@cdp], or alternatively along the lines of [@wati].

Potentials for bulk moduli
--------------------------

Let us denote the three (complex) bulk moduli as $t_1$, $t_2$, $t_3$. These moduli fields (which are related to the $a_i$ in in the usual way [@Candelas], [@Lerche]) represent the three complex structures of $T^6=(T^2)^3$. At this point we will write the formulas with all $t_i$’s in place and consider the case $t_1=t_2=t_3$ later on for calculational simplicity (though we would like to conjecture that our conclusions also hold for the more generic situation).

Let us first describe the superpotentials and Kähler potentials that are needed to describe the constraining equations for the bulk moduli. The type IIB flux superpotential [^4] $$W = \int (H_{RR} - \tau H_{NS}) \wedge\Omega = W_{RR}- \tau W_{NS},$$ is described in terms of complex structure moduli and the dilaton, while Kähler structure moduli do not appear. Here $\Omega$ denotes the holomorphic three form of the internal space and $\tau=C_0+ie^{-\phi}$ is the axio-dilaton combination. Let us rewrite this superpotential in terms of the bulk moduli by expanding the three form fluxes in terms of a cohomology 