  In effective supergravity theories following from the superstring, a modulus
field can quite naturally set the neccessary initial conditions for successful
cosmological inflation to be driven by a hidden sector scalar field. The
leading term in the scalar potential is {\em cubic} hence the spectrum of
scalar density perturbations neccessarily deviates from scale-invariance, while
the generation of gravitational waves is negligible. The growth of large-scale
structure is then consistent with observational data assuming a critical
density cold dark matter universe, with no need for a component of hot dark
matter. The model can be tested thorough measurements of cosmic microwave
background anisotropy on small angular scales.
