realistic models of spontaneous susy breaking requires two different sets of superfields, one of which participate in Standard Model gauge interactions and the other consists of singlets under the SM gauge group. The singlet fields usually have very large VEV and constitute the hidden sector of the theory. Such a sector has it’s natural origin in the framework of string theory. In a formalism where the matter fields of the MSSM constituting the observable sector are assumed to couple with the hidden sector singlets via gravitational interactions, spontaneous susy breaking in the hidden sector results into generation of soft-susy breaking terms in the observable sector[@soni; @ibanez]. If the local susy breaking is expected at a scale $\Lambda$, the soft terms would have a scale of order $\Lambda^2/M_p$, where $M_p$ is the Planck mass. Considering $\Lambda \sim 10^{11}~\rm GeV$, soft supersymmetry breaking terms $\sim$ TeV can be produced at the observable sector. Supergravity models however are often encountered with the existence of flat directions in the hidden sector. It is therefore necessary to lift the flat directions by appropriate mechanism.

While normally SUSY breaking leads to appearance of non-vanishing vacuum energy, some of the of the SUGRA models may have broken 