Consistency condition for inflation from (broken) conformal symmetry
  We investigate the symmetry constraints on the bispectrum, i.e. the
three-point correlation function of primordial density fluctuations, in
slow-roll inflation. It follows from the defining property of slow-roll
inflation that primordial correlation functions inherit most of their structure
from weakly broken de Sitter symmetries. Using holographic techniques borrowed
from the AdS/CFT correspondence, the symmetry constraints on the bispectrum can
be mapped to a set of stress-tensor Ward identities in a weakly broken
2+1-dimensional Euclidean CFT. We construct the consistency condition from
these Ward identities using conformal perturbation theory. This requires a
second order Ward identity and the use of the evolution equation. Our result
also illustrates a subtle difference between conformal perturbation theory and
the slow roll expansion.
