In-in and $\delta N$ calculations of the bispectrum from non-attractor
  single-field inflation
  In non-attractor single-field inflation models producing a scale-invariant
power spectrum, the curvature perturbation on super-horizon scales grows as
${\cal R}\propto a^3$. This is so far the only known class of self-consistent
single-field models with a Bunch-Davies initial state that can produce a large
squeezed-limit bispectrum violating Maldacena's consistency relation. Given the
importance of this result, we calculate the bispectrum with three different
methods: using quantum field theory calculations in two different gauges, and
classical calculations (the $\delta N$ formalism). All the results agree,
giving the local-form bispectrum parameter of
$f^{local}_{NL}=5(1+c_s^2)/(4c_s^2)$. This result is valid for arbitrary values
of the speed of sound parameter, $c_s$, for a particular non-attractor model we
consider in this paper.
