Multi-chaotic inflation with and without spectator field
  Motivated by the result of Planck+BICEP/Keck recently released, we
investigate the consistency of the multi-field inflation models in terms of the
spectral index $n_s$ and the tensor-to-scalar ratio $r$. In this study, we
focus on double-inflaton models with and without a spectator field. We find
that inflaton with a quadratic potential can become viable when three fields
with a specific hierarchical mass spectrum are realized such that two fields
act as inflatons and the other one is the spectator. We also discuss the
conditions to avoid the fine-tuning, by careful study of how the prediction
depends on the background trajectory in the inflaton-field space.
