Quantum coherence of cosmological perturbations

Understand

The degrees of quantum coherence of cosmological perturbations of different spins are computed in the large-scale limit and compared with the standard results holding for a single mode of the electromagnetic field in an optical cavity.

• The degree second-order coherence of curvature inhomogeneities (and, more generally, of the scalar modes of the geometry) reproduces faithfully the optical limit.
• For the vector and tensor fluctuations the numerical values of the normalized degrees of second-order coherence in the zero-time delay limit are always larger than unity (which is the Poisson benchmark value) but differ from the corresponding expressions obtainable in the framework of the single-mode approximation.
• General lessons are drawn on the quantum coherence of large-scale cosmological fluctuations.