  The quantization of the massless minimally coupled (mmc) scalar field in de
Sitter spacetime is known to be a non-trivial problem due to the appearance of
strong infrared (IR) effects. In particular, the scale-invariance of the CMB
power-spectrum - certainly one of the most successful predictions of modern
cosmology - is widely believed to be inconsistent with a de Sitter invariant
mmc two-point function.
  Using a Cesaro-summability technique to properly define an otherwise
divergent Fourier transform, we show in this Letter that de Sitter symmetry
breaking is \emph{not} a necessary consequence of the scale-invariant
fluctuation spectrum. We also generalize our result to the tachyonic scalar
fields, i.e the discrete series of representations of the de Sitter group, that
suffer from similar strong IR effects.

General Relativity and Quantum Cosmology;High Energy Physics - Theory