Producing a Scale-Invariant Spectrum of Perturbations in a Hagedorn   Phase of String Cosmology
  We study the generation of cosmological perturbations during the Hagedorn phase of string gas cosmology. Using tools of string thermodynamics we provide indications that it may be possible to obtain a nearly scale-invariant spectrum of cosmological fluctuations on scales which are of cosmological interest today. In our cosmological scenario, the early Hagedorn phase of string gas cosmology goes over smoothly into the radiation-dominated phase of standard cosmology, without having a period of cosmological inflation. 
Ali Nayeri, Robert H. Brandenberger and Cumrun Vafa