We study the generation of primordial perturbations in a ( single-field ) slow-roll inflationary universe .
In momentum space , these ( Gaussian ) perturbations are characterized by a zero mean and a non-zero variance \Delta ^ { 2 } ( k,t ) .
However , in position space the variance diverges in the ultraviolet .
The requirement of a finite variance in position space forces one to regularize \Delta ^ { 2 } ( k,t ) .
This can ( and should ) be achieved by proper renormalization in an expanding universe in a unique way .
This affects the predicted scalar and tensorial power spectra ( evaluated when the modes acquire classical properties ) for wavelengths that today are at observable scales .
As a consequence , the imprint of slow-roll inflation on the CMB anisotropies is significantly altered .
We find a non-trivial change in the consistency condition that relates the tensor-to-scalar ratio r to the spectral indices .
For instance , an exact scale-invariant tensorial power spectrum , n _ { t } = 0 , is now compatible with a non-zero ratio r \approx 0.12 \pm 0.06 , which is forbidden by the standard prediction ( r = -8 n _ { t } ) .
The influence of relic gravitational waves on the CMB may soon come within the range of planned measurements , offering a non-trivial test of the new predictions .