Equilateral Non-Gaussianity and New Physics on the Horizon
  We examine the effective theory of single-field inflation in the limit where
the scalar perturbations propagate with a small speed of sound. In this case
the non-linearly realized time-translation symmetry of the Lagrangian implies
large interactions, giving rise to primordial non-Gaussianities. When the
non-Gaussianities are measurable, these interactions will become strongly
coupled unless new physics appears close to the Hubble scale. Due to its
proximity to the Hubble scale, the new physics is not necessarily decoupled
from inflationary observables and can potentially affect the predictions of the
model. To understand the types of corrections that may arise, we construct
weakly-coupled completions of the theory and study their observational
signatures.
