On the new string theory inspired mechanism of generation of   cosmological perturbations
  Recently a non-inflationary mechanism of generation of scale-free cosmological perturbations of metric was proposed by Brandenberger, Nayeri, and Vafa in the context of the string gas cosmology. We discuss various problems of their model and argue that the cosmological perturbations of metric produced in this model have blue spectrum with a spectral index n = 5, which strongly disagrees with observations. We conclude that this model in its present form is not a viable alternative to inflationary cosmology. 
Nemanja Kaloper, Lev Kofman, Andrei Linde and Viatcheslav Mukhanov