  The curvature inhomogeneities are systematically scrutinized in the framework
of the Glauber approach. The amplified quantum fluctuations of the scalar and
tensor modes of the geometry are shown to be first-order coherent while the
interference of the corresponding intensities is larger than in the case of
Bose-Einstein correlations. After showing that the degree of second-order
coherence does not suffice to characterize unambiguously the curvature
inhomogeneities, we argue that direct analyses of the degrees of third and
fourth-order coherence are necessary to discriminate between different
correlated states and to infer more reliably the statistical properties of the
large-scale fluctuations. We speculate that the moments of the multiplicity
distributions of the relic phonons might be observationally accessible thanks
to new generations of instruments able to count the single photons of the
Cosmic Microwave Background in the THz region.
