Squeezed Bispectrum in the $\delta N$ Formalism: Local Observer Effect
  in Field Space
  The prospects of future galaxy surveys for non-Gaussianity measurements call
for the development of robust techniques for computing the bispectrum of
primordial cosmological perturbations. In this paper, we propose a novel
approach to the calculation of the squeezed bispectrum in multiple-field
inflation. With use of the $\delta N$ formalism, our framework sheds new light
on the recently pointed out difference between the squeezed bispectrum for
global observers and that for local observers, while allowing one to calculate
both. For local observers in particular, the squeezed bispectrum is found to
vanish in single-field inflation. Furthermore, our framework allows one to go
beyond the near-equilateral ("small hierarchy") limit, and to automatically
include intrinsic non-Gaussianities that do not need to be calculated
separately. The explicit computational programme of our method is given and
illustrated with a few examples.
