Exact Mapping between Tensor and Most General Scalar Power Spectra
  We prove an exact relation between the tensor and the scalar primordial power
spectra generated during inflation. Such a mapping considerably simplifies the
derivation of any power spectra as they can be obtained from the study of the
tensor modes only, which are much easier to solve. As an illustration, starting
from the second order slow-roll tensor power spectrum, we derive in a few lines
the next-to-next-to-leading order power spectrum of the comoving curvature
perturbation in generalized single field inflation with a varying speed of
sound.
