The string coupling accelerates the expansion of the universe

摘要

Generic cosmological models in non-critical string theory have a time-dependent dilaton background at a late epoch. The cosmological deceleration parameter q(0) is given by the square of the string coupling, g(s)(2), up to a negative sign. Hence, the expansion of the universe must accelerate eventually, and the observed value of q(0) corresponds to g(s)(2) similar to 0.6. In this scenario, the string coupling is asymptotically free at large times, but its present rate of change is imperceptibly small.