  We analyse slow-roll inflationary cosmologies that are holographically dual
to a three-dimensional conformal field theory deformed by a nearly marginal
scalar operator. We show the cosmological power spectrum is inversely
proportional to the spectral density associated with the 2-point function of
the trace of the stress tensor in the deformed CFT. Computing this quantity
using second-order conformal perturbation theory, we obtain a holographic power
spectrum in exact agreement with the expected inflationary power spectrum to
second order in slow roll.
