Super cosmic variance from mode-coupling: A worked example
  If the entire post-inflationary patch is large compared to our Hubble volume
even a small level of non-Gaussianity can cause statistics of the primordial
curvature field in our Hubble volume to be biased by mode-coupling. We
explicitly compute the variation of locally measured statistics of the
primordial curvature $\zeta$ from non-Gaussian mode coupling within a specific
inflationary scenario: the curvaton model with a quadratic curvaton potential.
This "super cosmic variance" is calculated in two ways: (i) as a super observer
who has access to the curvature perturbation field across the entire
post-inflationary patch and therefore sees local statistics as biased by mode
coupling and (ii) as a local observer who sees the statistics of $\zeta$
determined by the local values of quantities in their Hubble patch. The two
calculations agree and show that in the quadratic curvaton model patch-to-patch
differences in statistics of $\zeta$ can be interpreted entirely as a shift in
the value of the curvaton field at freeze out. Applying the same arguments to
single-field slow-roll inflation gives a simple picture of how non-Gaussian
mode-coupling between the curvature perturbations on very different physical
scales must vanish in the attractor limit.
