"Characterizing inflationary perturbations: The Uniform approximation"
Habib, S. ", Heinen, A., Heitmann, K., Jungman, G., & Molina-Paris, C. (2004). "Characterizing inflationary perturbations: The Uniform approximation". "Phys. Rev. D", "70", "083507". http://doi.org/"10.1103/PhysRevD.70.083507" (Original work published Juni 2004)