Mixed inflaton and spectator field models: CMB constraints and μ distortion

We discuss mixed inflaton and spectator field models where both the fields are responsible for the observed density fluctuations. We combine the angular power spectrum of the CMB temperature anisotropy from the Planck 2013 result and other ground-based CMB observations in order to constrain both the general mixed model as well as some specific representative scenarios. Based on the Markov Chain Monte Carlo method, in addition to constraints on model parameters, we obtain the predictive posterior distributions of the CMB spectral mu distortion for those models. We demonstrate that the standard single-field inflaton model typically predicts mu similar to 10(-8) with a relatively narrow distribution, whereas for the mixed models, the distribution turns out to be much broader, and mu could be larger by almost an order of magnitude. Hence future experiments of mu distortion could provide a tool for the critical testing of the mixed source models of the primordial perturbation.