Towards a solution of the moduli problems of string cosmology

There rue at least two serious moduli problems in string cosmology The firs t is the possibility that moduli dominate the energy density at the time of nucleosynthesis. The second is that they may not find their minima all tog ether. After reviewing some previously proposed solutions to these problems , we propose another: all of the moduli but the dilaton sit at points of en hanced symmetry. The dilaton has a potential similar to those of racetrack models; it is very massive and its dynamics do not break supersymmetry. The dilaton is able to find the minimum of its potential because the energy is dominated by non-zero momentum modes. This energy need not be thermal. The effective potential for the dilaton is quite different from its flat space form. If certain conditions are satisfied, the dilaton settles into the de sired minimum; if not, it is forced to weak coupling. (C) 2000 Published by Elsevier Science B.V. All rights reserved.