Role of the curvaton after the last Planck dataset

The expected improvements in the precision of inflationary physics observables including the scalar spectral index ns and the tensor-to-scalar ratio r will reveal more than just the viability of a particular model of inflation. In the presence of a curvaton field χ, supposedly dead models of inflation can be resurrected, as these observables are affected by curvaton perturbations. For currently successful models, improved constraints will enable us to constrain the properties of extra decaying scalar degrees of freedom produced during inflation. In this work, we demonstrate these diverse uses of a curvaton field with the most recent constraints on (ns,r) and two exemplary inflation models, a Starobinsky-like model and a model of new inflation. The specific models used as examples can be derived in the context of supergravity. Our analysis invokes three free parameters: the curvaton mass mχ, its decay rate Γχ, and the reheating temperature TRH produced by inflaton decays. We systematically analyze possible postinflationary era scenarios of a curvaton field. By projecting the most recent cosmic microwave background (CMB) data on (ns,r) into this parameter space, we can either set constraints on the curvaton parameters from successful models of inflation (so that the success is not spoiled) or determine the parameters that are able to save a model for which ns is predicted to be below the experimental data. We emphasize that the initial value of χ2 H4/mχ2 produced during inflation is determined from a stochastic approach and thus not a free parameter in our analysis. We also investigate the production of local non-Gaussianity fNL(loc) and apply current CMB constraints to the parameter space. Intriguingly, we find that a large value of fNL(loc) of O(1) can be produced for both of the two representative inflation models.