Does Planck Actually "See" the Bunch-Davies State?

TL;DR

This paper investigates whether Planck satellite data can distinguish the standard Bunch-Davies state from an entangled state of scalar fluctuations, showing that current observations may already constrain such deviations.

Contribution

It introduces a model with an entangled state of scalar fluctuations, compares its predictions with the Bunch-Davies state, and discusses potential observational bounds from Planck data.

Findings

Entangled states can produce power spectra consistent with Planck data.

Existing data may constrain deviations from the Bunch-Davies state.

Differences in CMB anisotropies could reveal the quantum nature of inflationary fluctuations.

Abstract

To what extent can the Planck satellite observations be interpreted as confirmation of the quantum part of the inflationary paradigm? Has it "seen" the Bunch-Davies state? We compare and contrast the Bunch-Davies interpretation with one using a so-called entangled state in which the fluctuations of a spectator scalar field are entangled with those of the metric perturbations $\zeta$. We first show how a spectator scalar field $\Sigma$, with an expectation value $\sigma(t)$ that evolves in time, will generically generate such a state. We then use this state to compute the power spectrum $P_{\zeta}(k)$ and thence the temperature anisotropies $C_l$ in the Cosmic Microwave Background (CMB). We find interesting differences from the standard calculations using the Bunch-Davies (BD) state. We argue that existing data may already be used to place interesting bounds on this class of deviations from the BD state and that, for some values of the parameters of the state, the power spectra may be consistent with the Planck satellite data.