\documentclass[12pt]{article}
\usepackage{amsmath,amssymb,amsfonts}
\begin{document}
The recent detection of the primordial gravitational waves from the BICEP2 observation seems to be in tension with the upper bound on the amplitude of tensor perturbations from the PLANCK data. We consider a phenomenological model of inflation in which the microscopical properties of the inflationary fluid such as the equation of state w or the sound speed cs jump in a sharp manner. We show that the amplitude of the scalar perturbations is controlled by a non-trivial combination of w and csbefore and after the phase transition while the tensor perturbations remains nearly intact. With an appropriate choice of the fluid parameters w and cs one can suppress the scalar perturbation power spectrum on large scales to accommodate a large tensor amplitude with r=0.2 as observed by BICEP2 observation.
\end{document}