  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 $r\approx 0.12\pm0.06$, which is forbidden
by the standard prediction ($r=-8n_t$). 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.
