On the phase-space volume of primordial cosmological perturbations

We show how to determine the typical phase-space volume, , for primordial gravitational waves produced during an inflationary stage, which is invariant under squeezing. An expression for is found in the long wavelength regime. The quasi-classical entropy of a pure vacuum initial state defined as the logarithm of modulo a constant remains zero in spite of the generation of fluctuations (creation of real gravitons).