Cosmological perturbations from a Spectator field during inflation
  In this paper we will discuss analytically the perturbations created from a
slowly rolling subdominant spectator field which decays much before the end of
inflation. The quantum fluctuations of such a spectator field can seed
perturbations on very large scales and explain the temperature anisotropy in
the cosmic microwave background radiation with moderate non-Gaussianity,
provided the relevant modes leave the Hubble patch while the spectator is
slowly rolling. Furthermore, the perturbations are purely {\it adiabatic} since
the inflaton decay dominates and creates all the Standard Model degrees of
freedom. We will provide two examples for the spectator field potential, one
with a step function profile, and the other with an inflection point. In both
the cases we will compute higher order curvature perturbations, i.e.\ local
bispectrum and trispectrum, which can be constrained by the forthcoming Planck
data.
