Mixed Inflaton and Spectator Field Models after Planck
  We investigate the possibility that the primordial perturbation has two
sources: the inflaton and a spectator field, which is not dynamically important
during inflation but which after inflation can contribute to the curvature
perturbation. The recent Planck results on the power spectrum and
non-Gaussianity allow us to put constraints on such mixed models. In the
generic case, where no specific model for the inflaton or the spectator is
assumed, one finds that in the mixed scenario it is possible to have a large
trispectrum with tau_NL >> (f_NL)^2. The constraints on inflation models in the
plane of the spectral index and tensor-to-scalar ratio are modified by the
presence of a spectator and depend also on the ratio of the
spectator-to-inflaton power R. If one chooses the spectator to be the curvaton
with a quadratic potential, non-Gaussianities can be computed and imply
restrictions on possible values of R. We also consider a mixed curvaton and
chaotic inflation model and show that even quartic chaotic inflation is still
feasible in the context of mixed models.
