Cosmological and Wormhole Solutions in Low-Energy Effective String Theory

We derive and study a class of cosmological and wormhole solutions of low-energy effective string field theory. We consider a general four-dimensional string effective action where moduli of the compactified manifold and the electromagnetic field are present. The cosmological solutions of the two-dimensional effective theory obtained by dimensional reduction of the former are discussed. In particular we demonstrate that the two-dimensional theory possesses a scale-factor duality invariance. Euclidean four-dimensional instantons describing the nucleation of the baby universes are found and the probability amplitude for the nucleation process is given.