On Primordial Perturbations of Test Scalar Fields
  The primordial perturbations of test scalar fields not affecting the evolution of background may be very interesting since they can be transferred to the curvature perturbations by some mechanisms, and thus under certain condition can be responsible for the structure formation of observable universe. In this brief report we study the primordial perturbations of test scalar fields in various (super)accelerated expanding backgrounds. 
Yun-Song Piao and Yuan-Zhong Zhang