From the Spectrum to Inflation : An Inverse Formula for the General   Slow-Roll Spectrum
  We propose a general inverse formula for extracting inflationary parameters from the observed power spectrum of cosmological perturbations. Under the general slow-roll scheme, which helps to probe the properties of inflation in a model independent way, we invert the leading order, single field, power spectrum formula. We also give some physically interesting examples to demonstrate its wide applicability and illuminate its properties. 
Minu Joy, Ewan D. Stewart, Jinn-Ouk Gong, Hyun-Chul Lee