Exact solution in a string cosmological model

We construct an exact solution of the Friedmann equations with a phantom scalar matter field originating in string field theory and show the absence of the big-rip singularity. The notable features of the model are a ghost sign of the kinetic term and a special polynomial form of the effective tachyon potential. The constructed solution is stable under small fluctuations of the initial conditions and special variations of the form of the potential.