  During inflation, the geometry of spacetime is described by a (quasi-)de
Sitter phase. Inflationary observables are determined by the underlying (softly
broken) de Sitter isometry group SO(1, 4) which acts like a conformal group on
R^3: when the fluctuations are on super-Hubble scales, the correlators of the
scalar fields are constrained by conformal invariance. Heavy fields with mass m
larger than the Hubble rate H correspond to operators with imaginary dimensions
in the dual Euclidean three-dimensional conformal field theory. By making use
of the dS/CFT correspondence we show that, besides the Boltzmann suppression
expected from the thermal properties of de Sitter space, the generic effect of
heavy fields in the inflationary correlators of the light fields is to
introduce power-law suppressed corrections of the form O(H^2/m^2). This can be
seen, for instance, at the level of the four-point correlator for which we
provide the correction due to a massive scalar field exchange.
