One-particle-irreducible consistency relations for cosmological
  perturbations
  We derive consistency relations for correlators of scalar cosmological
perturbations which hold in the "squeezed limit" in which one or more of the
external momenta become soft. Our results are formulated as relations between
suitably defined one-particle irreducible N-point and (N-1)-point functions
that follow from residual spatial conformal diffeomorphisms of the unitary
gauge Lagrangian. As such, some of these relations are exact to all orders in
perturbation theory, and do not rely on approximate deSitter invariance or
other dynamical assumptions (e.g., properties of the operator product expansion
or the behavior of modes at horizon crossing). The consistency relations apply
model-independently to cosmological scenarios where the time evolution is
driven by a single scalar field. Besides reproducing the known results for
single-field inflation in the slow roll limit, we verify that our consistency
relations hold more generally, for instance in ghost condensate models in flat
space. We comment on possible extensions of our results to multi-field models.
