Infinity in string cosmology: A review through open problems
  We review recent developments in the field of string cosmology with particular emphasis on open problems having to do mainly with geometric asymptotics and singularities. We discuss outstanding issues in a variety of currently popular themes, such as tree-level string cosmology asymptotics, higher-order string correction effects, M-theory cosmology, braneworlds, and finally ambient cosmology. 
Ignatios Antoniadis, Spiros Cotsakis
hep-th gr-qc