The Primordial Perturbation Spectrum from Various Expanding and   Contracting Phases
  In this paper, focusing on the case of single scalar field, we discuss various expanding and contracting phases generating primordial perturbations, and study the relation between the primordial perturbation spectrum from these phases and the parameter w of state equation in details. Furthermore, we offer an interesting classification for the primordial perturbation spectrum from various phases, which may have important implications for building an early universe scenario embedded in possible high energy theories. 
Yun-Song Piao and Yuan-Zhong Zhang