Impact of quantum entanglement on spectrum of cosmological fluctuations

TL;DR

This paper explores how quantum entanglement between causally separated regions in de Sitter space influences the spectrum of cosmological vacuum fluctuations, revealing scale-dependent effects on the fluctuation spectrum.

Contribution

It demonstrates the impact of quantum entanglement on the shape of the fluctuation spectrum in de Sitter space, especially on large scales, using a reduced density matrix approach.

Findings

Scale invariant spectrum on small scales for massless scalar fields

Entanglement modifies the spectrum shape on large scales

Quantum effects become significant near the curvature radius

Abstract

We investigate the effect of entanglement between two causally separated open charts in de Sitter space on the spectrum of vacuum fluctuations. We consider a free massive scalar field, and construct the reduced density matrix by tracing out the vacuum state for one of the open charts, as recently derived by Maldacena and Pimentel. We formulate the mean-square vacuum fluctuations by using the reduced density matrix and show that the scale invariant spectrum of massless scalar field is realized on small scales. On the other hand, we find that the quantum entanglement affects the shape of the spectrum on large scales comparable to or greater than the curvature radius.