Unifying attractor and non-attractor models of inflation under a single soft theorem

We derive the bispectrum's squeezed limit of primordial curvature perturbations in canonical single field inflation valid to all orders in slow-roll parameters. Our derivation relies exclusively on the diffeomorphism invariance of canonical single field inflation, and does not require taking into account de Sitter isometries or shift symmetries of the ultraviolet theory in which inflation is build upon. Our result consists in the standard Maldacena's consistency relation (proportional to the spectral index of the power spectrum) plus additional terms containing time derivatives of the power spectrum. An important consequence of our result is the conclusion that a non-attractor phase (e.g. ultra slow roll phase) cannot generate large non-Gaussianity at the end of inflation. This is because as soon as the non-attractor phase finishes, the amplitudes of super-horizon modes stop growing, and one recovers Maldacena's consistency relation. Thus, we claim that a robust prediction from canonical single field inflation (attractor or non-attractor) is that the observable squeezed limit of primordial non-Guassianity vanishes exactly.