Suppression of the large scale curvature perturbation by interacting   fluids
  The large-scale dynamics of a two-fluid system with a time dependent interaction is studied analytically and numerically. We show how a rapid transition can significantly suppress the large-scale curvature perturbation and present approximative formulae for estimating the effect. By comparing to numerical results, we study the applicability of the approximation and find good agreement with exact calculations. 
T. Multamaki, J. Sainio, I. Vilja