Extended Slow-Roll Conditions and Rapid-Roll Conditions
  We derive slow-roll conditions for a scalar field which is non-minimally coupled with gravity in a consistent manner and express spectral indices of scalar/tensor perturbations in terms of the slow-roll parameters. The conformal invariance of the curvature perturbation is proved without linear approximations. Rapid-roll conditions are also derived, and the relation with the slow-roll conditions is discussed. 
Takeshi Chiba, Masahide Yamaguchi