Nonsingular dilaton cosmology in the string frame

We consider the theory obtained by adding to the usual string frame dilaton gravity action specially constructed higher derivative terms motivated by the limited curvature construction of [1] and determine the spatially homogeneous and isotropic solutions to the resulting equations of motion. All solutions of the resulting theory of gravity with these symmetries are nonsingular and all curvature invariants are bounded. For initial conditions inspired by the pre-big-bang scenario solutions exist which correspond to a spatially at Universe starting in a dilaton-dominated superinationary phase with (H) over dot >0 and having a smooth transition to an expanding Friedmann Universe with (H) over dot <0. Hence, the graceful exit problem of pre-big-bang cosmology is solved in a natural way.