The curvaton scenario is one of the simplest and most widely studied alternatives to single-field inflation. Even though the perturbations are not generated by the inflaton and the thermal history of the universe is very different from the end of inflation until the curvaton decays, observations are still unable to distinguish between the two scenarios. However the curvaton can produce a much richer phenomenology than single-field inflation.
We carry out a comprehensive analysis of the simplest curvaton model, which is based on two non-interacting massive fields. Our analysis encompasses cases where the inflaton and curvaton both contribute to observable perturbations, and where the curvaton itself drives a second period of inflation. We consider both power spectra and non-Gaussianity observables, and focus on presenting constraints in model parameter space. If confirmed, the recent BICEP2 results require that the inflaton perturbations provide a significant fraction of the total perturbation, ruling out the original curvaton scenario in which the inflaton perturbations are negligible, though not the admixture regime where both inflaton and curvaton contribute to the power spectrum.
