Cosmic backgrounds of relic gravitons and their absolute normalization
  Provided the consistency relations are not violated, the recent Bicep2
observations pin down the absolute normalization, the spectral slope and the
maximal frequency of the cosmic graviton background produced during inflation.
The properly normalized spectra are hereby computed from the lowest frequencies
(of the order of the present Hubble rate) up to the highest frequency range in
the GHz region. Deviations from the conventional paradigm cannot be excluded
and are examined by allowing for different physical possibilities including, in
particular, a running of the tensor spectral index, an explicit breaking of the
consistency relations and a spike in the high-frequency tail of the spectrum
coming either from a post-inflationary phase dominated by a stiff fluid of from
the contribution of waterfall fields in a hybrid inflationary context. The
direct determinations of the tensor to scalar ratio at low frequencies, if
confirmed by the forthcoming observations, will also affect and constrain the
high-frequencies uncertainties. The limits on the cosmic graviton backgrounds
coming from wide-band interferometers (such as Ligo/Virgo, Lisa and Bbo/Decigo)
together with a more accurate scrutiny of the tensor B mode polarization at low
frequencies will set direct bounds on the post-inflationary evolution and on
other unconventional completions of the standard lore.
