The (not so) squeezed limit of the primordial 3-point function

Understand

We prove that, in a generic single-field model, the consistency relation for the 3-point function in the squeezed limit receives corrections that vanish quadratically in the ratio of the momenta, i.e.

• as (k_L/k_S)^2.
• This implies that a detection of a bispectrum signal going as 1/k_L^2 in the squeezed limit, that is suppressed only by one power of k_L compared with the local shape, would rule out all single-field models.
• The absence of this kind of terms in the bispectrum holds also for multifield models, but only if all the fields have a mass much smaller than H.