CMB from CFT
  During inflation, spacetime is approximately described by de Sitter space
which is conformally invariant with the symmetry group SO(1,4). This symmetry
can significantly constrain the quantum perturbations which arise in the
inflationary epoch. We consider a general situation of single field inflation
and show that the three point function involving two scalar modes and one
tensor mode is uniquely determined, up to small corrections, by the conformal
symmetries. Special conformal transformations play an important role in our
analysis. Our result applies only to models where the inflaton sector also
approximately preserves the full conformal group and shows that this three
point function is a good way to test if special conformal invariance was
preserved during inflation.
