  We consider the effects on the primordial power spectrum of a period of
radiation-dominated expansion prior to the inflationary era. If inflation lasts
a total of only 60 e-folds or so, the boundary condition for quantum modes
cannot be taken in the short-wavelength limit as in the standard perturbation
calculation. Instead, the boundary condition is set by the vacuum state of the
prior radiation-dominated epoch, which only corresponds to the inflationary
vacuum state in the ultraviolet limit. This altered vacuum state results in a
modulation of the inflationary power spectrum. We calculate the modification to
a best-fit model from the WMAP3 data set, and find that power is suppressed at
large scales. The modified power spectrum is favored only very weakly by the
data.
