How the curvaton scenario, modulated reheating and an inhomogeneous end of inflation are related

Abstract: In this paper we analyse three models of the early universe, for which the respective mechanisms for generating the curvature perturbation are considered disparate. We find that in fact the mechanisms are very similar, and hence explain why they give rise to a large non-gaussianity. We show that the mechanism for generating the primordial curvature perturbation, and hence the observable non-gaussianity, is similar in both the Curvaton and Modulated Reheating models. In both cases the model can be written in terms of an energy transfer between the constituting fluids. We then show that this is also true for the mechanism of generating the curvature perturbation by symmetry breaking the end of inflation. We then relate this to the non-gaussian contribution to the curvature perturbation and find that it is inversely proportional to the efficiency with which the curvature perturbation is transferred between the fluids. For the first time, we generalise models of modulated reheating to allow for a non-linear energy transfer rate.