Revisiting non-Gaussianity in non-attractor inflation models in the
  light of the cosmological soft theorem
  We revisit the squeezed-limit non-Gaussianity in the single-field
non-attractor inflation models from the viewpoint of the cosmological soft
theorem. In the single-field attractor models, inflaton's trajectories with
different initial conditions effectively converge into a single trajectory in
the phase space, and hence there is only one \emph{clock} degree of freedom
(DoF) in the scalar part. Its long-wavelength perturbations can be absorbed
into the local coordinate renormalization and lead to the so-called
\emph{consistency relation} between $n$- and $(n+1)$-point functions. On the
other hand, if the inflaton dynamics deviates from the attractor behavior, its
long-wavelength perturbations cannot necessarily be absorbed and the
consistency relation is expected not to hold any longer. In this work, we
derive a formula for the squeezed bispectrum including the explicit correction
to the consistency relation, as a proof of its violation in the non-attractor
cases. First one must recall that non-attractor inflation needs to be followed
by attractor inflation in a realistic case. Then, even if a specific
non-attractor phase is effectively governed by a single DoF of phase space
(represented by the exact ultra-slow-roll limit) and followed by a single-DoF
attractor phase, its transition phase necessarily involves two DoF in dynamics
and hence its long-wavelength perturbations cannot be absorbed into the local
coordinate renormalization. Thus, it can affect local physics, even taking
account of the so-called \emph{local observer effect}, as shown by the fact
that the bispectrum in the squeezed limit can go beyond the consistency
relation. More concretely, the observed squeezed bispectrum does not vanish in
general for long-wavelength perturbations exiting the horizon during a
non-attractor phase.
