Modifications in the Spectrum of Primordial Gravitational Waves Induced
  by Instantonic Fluctuations
  Vacuum to vacuum instantonic transitions modify the power spectrum of
primordial gravitational waves. We evaluate the new form of the power spectrum
for ordinary gravity as well as the parity violation induced in the spectrum by
a modification of General Relativity known as Holst term and we outline the
possible experimental consequences.
