Quantum coherence of cosmological perturbations

TL;DR

This paper investigates the quantum coherence properties of cosmological perturbations across different spins, revealing that scalar modes behave like optical fields while vector and tensor modes exhibit higher-than-Poisson coherence, providing insights into the quantum nature of early universe fluctuations.

Contribution

It extends the analysis of quantum coherence to cosmological perturbations of various spins, comparing with optical limits and highlighting differences in vector and tensor modes.

Findings

Scalar modes reproduce optical second-order coherence.

Vector and tensor modes have coherence values larger than unity.

Differences from single-mode approximations are identified.

Abstract

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.