A new method for calculating the primordial bispectrum in the squeezed
  limit
  In 2004, Creminelli and Zaldarriaga proposed a consistency relation for the
primordial curvature perturbation of all single-field inflation models; it
related the bispectrum in the squeezed limit to the spectral tilt. We have
developed a technique, based in part on the Creminelli and Zaldarriaga
argument, that can greatly simplify the calculation of the squeezed-limit
bispectrum using the in-in formalism; we were able to arrive at a generic
formula that does not rely on a slow-roll approximation. Using our formula, we
explicitly tested the consistency relation for power-law inflation and for an
exactly scale-invariant model by Starobinsky; for the latter model, Creminelli
and Zaldarriaga's argument predicts a vanishing bispectrum whereas our quantum
calculation shows a non-zero bispectrum that approaches zero in the
long-wavelength limit and for inflation with a large number of e-folds.
