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| Paper IPM / Astronomy / 13671 |
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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.
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