A New Approach to String Cosmology
  We discuss quotients of Anti-de Sitter (AdS) spacetime by a discrete group in light of the AdS-CFT correspondence. Some quotients describe closed universes which expand from zero volume to a maximum size and then contract. Maldacena's conjecture suggests that they should be represented in string theory by suitable quotients of the boundary conformal field theory. We discuss the required identifications, and construct the states associated with the linearized supergravity modes in the cosmological background. 
Gary T. Horowitz and Donald Marolf