Quantum Discord of Cosmic Inflation: Can we Show that CMB Anisotropies are of Quantum-Mechanical Origin?. (arXiv:1510.04038v7 [astro-ph.CO] UPDATED)

We investigate the quantumness of primordial cosmological fluctuations and
its detectability. The quantum discord of inflationary perturbations is
calculated for an arbitrary splitting of the system, and shown to be very large
on super-Hubble scales. This entails the presence of large quantum
correlations, due to the entangled production of particles with opposite
momentums during inflation. To determine how this is reflected at the
observational level, we study whether quantum correlators can be reproduced by
a non-discordant state, i.e. a state with vanishing discord that contains
classical correlations only. We demonstrate that this can be done for the power
spectrum, the price to pay being twofold: first, large errors in other
two-point correlation functions and second, the presence of intrinsic
non-Gaussianity. The detectability of these two features remains to be
determined but could possibly rule out a non-discordant description of the
cosmic microwave background. If one abandons the idea that perturbations should
be modeled by quantum mechanics and wants to use a classical stochastic
formalism instead, we show that any two-point correlators on super-Hubble
scales can be exactly reproduced regardless of the squeezing of the system. The
latter becomes important only for higher-order correlation functions that can
be accurately reproduced only in the strong squeezing regime.

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