Entanglement masquerading in the CMB

TL;DR

This paper investigates whether entangled quantum states generated during inflation can be distinguished from the standard Bunch-Davies state using Planck CMB data, developing a perturbative framework for analysis.

Contribution

The authors develop a systematic perturbative framework to constrain or detect entangled inflationary states with CMB data, extending previous theoretical work.

Findings

Most entangled states considered are consistent with current data

The framework can be expanded to explore a wider variety of entangled states

Current data does not strongly favor or exclude entangled states over the Bunch-Davies state

Abstract

The simplest single-field inflation models capture all the relevant contributions to the patterns in the Cosmic Microwave Background (CMB) observed today. A key assumption in these models is that the quantum inflationary fluctuations that source such patterns are generated by a particular quantum state -- the Bunch-Davies (BD) state. While this is a well-motivated choice from a theoretical perspective, the question arises of whether current data can rule out other, also well motivated, choices of states. In particular, as we previously demonstrated in arXiv:2104.13410 [hep-th], entanglement is naturally and inevitably dynamically generated during inflation given the presence of a "rolling" spectator scalar field -- and the resulting entangled state will yield a primordial power spectrum with potentially measurable deviations compared to the canonical BD result. For this work we developed a perturbative framework to allow a systematic exploration of constraints on (or detection of) entangled states with Planck CMB data using Monte Carlo techniques. We have found that most entangled states accessible with our framework are consistent with the data. One would have to expand the framework to allow a greater variety of entangled states in order to saturate the Planck constraints and more systematically explore any preferences the data may have among the different possibilities.