The Observed Squeezed Limit of Cosmological Three-Point Functions
  The squeezed limit of the three-point function of cosmological perturbations
is a powerful discriminant of different models of the early Universe. We
present a conceptually simple and complete framework to relate any primordial
bispectrum in this limit to late time observables, such as the CMB temperature
bispectrum and the scale-dependent halo bias. We employ a series of convenient
coordinate transformations to capture the leading non-linear effects of
cosmological perturbation theory on these observables. This makes crucial use
of Fermi Normal Coordinates and their conformal generalization, which we
introduce here and discuss in detail. As an example, we apply our formalism to
standard slow-roll single-field inflation. We show explicitly that Maldacena's
results for the squeezed limits of the scalar bispectrum [proportional to
(ns-1) in comoving gauge] and the tensor-scalar-scalar bispectrum lead to no
deviations from a Gaussian universe, except for projection effects. In
particular, the primordial contributions to the squeezed CMB bispectrum and
scale dependent halo bias vanish, and there are no primordial "fossil"
correlations between long-wavelength tensor perturbations and small-scale
perturbations. The contributions to observed correlations are then only due to
projection effects such as gravitational lensing and redshift perturbations.
