Metric Perturbations and Inflationary Phase Transitions
  We study the out of equilibrium dynamics of inflationary phase transitions and compute the resulting spectrum of metric perturbations relevant to observation. We show that simple single field models of inflation may produce an adiabatic perturbation spectrum with a blue spectral tilt and that the precise spectrum depends on initial conditions at the outset of inflation. 
D. Cormier and R. Holman