Two-point correlators revisited: Fast and slow scales in multifield
  models of inflation
  We study the structure of two-point correlators of the inflationary field
fluctuations in order to improve the accuracy and efficiency of the existing
methods to calculate primordial spectra. We present a description motivated by
the separation of the fast and slow evolving components of the spectrum which
is based on Cholesky decomposition of the field correlator matrix. Our purpose
is to rewrite all the relevant equations of motion in terms of slowly varying
quantities. This is important in order to consider the contribution from
high-frequency modes to the spectrum without affecting computational
performance. The slow-roll approximation is not required to reproduce the main
distinctive features in the power spectrum for each specific model of
inflation.
