EVOLUTION OF A STRING NETWORK IN BACKGROUNDS WITH ROLLING HORIZONS

We discuss the temporal variation of the equation of state of a classical string network, evolving in a background in which the Hubble radius H⁻¹ shrinks to a minimum and then re-expands to infinity. We also present a method to look for self-consistent non-vacuum string backgrounds, corresponding to the simultaneous solution of the gravi-dilaton background equations and of the string equations of motion.