Cosmic variance in inflation with two light scalars
  We examine the squeezed limit of the bispectrum when a light scalar with
arbitrary non-derivative self-interactions is coupled to the inflaton. We find
that when the hidden sector scalar is sufficiently light ($m\lesssim0.1\,H$),
the coupling between long and short wavelength modes from the series of higher
order correlation functions (from arbitrary order contact diagrams) causes the
statistics of the fluctuations to vary in sub-volumes. This means that
observations of primordial non-Gaussianity cannot be used to uniquely
reconstruct the potential of the hidden field. However, the local bispectrum
induced by mode-coupling from these diagrams always has the same squeezed
limit, so the field's locally determined mass is not affected by this cosmic
variance.
