Mixed inflaton and curvaton perturbations

A recent variant of the inflationary paradigm is that the “primordial” curvature perturbations come from quantum fluctuations of a scalar field, subdominant and effectively massless during inflation, called the “curvaton”, instead of the fluctuations of the inflaton field. We consider a cosmological scenario which mixes the standard and variant versions, i.e. where primordial curvature perturbations are generated by quantum fluctuations of both an inflaton and a curvaton field. This is the case when the curvaton starts oscillating when it already contributes significantly to the total energy density in the universe. We compute the curvature perturbation and its spectrum in this scenario and we discuss the observational consequences.