EXACT SUPERSTRING MOTIVATED COSMOLOGICAL MODELS

We present a number of new, exact scalar field cosmologies where the potential consists of two or more exponential terms. Such potentials are motivated by supergravity or superstring models formulated in higher-dimensional spacetimes that have been compactified to 3 + 1 dimensions. We have found solutions in both curved and flat Robertson-Walker spacetimes. These models have a diverse range of properties and often possess several distinct phases, with a smooth transition between ordinary and inflationary expansion. While exponential potentials typically produce power-law inflation, we find models where the inflationary period contains eras of both power-law and exponential growth.