Decoherence Can Relax Cosmic Acceleration: an Example

TL;DR

This paper explores how considering only observable states in de Sitter space leads to thermal particle production and causes the space to become unstable, potentially relaxing cosmic acceleration.

Contribution

It introduces a new approach focusing on observable states, revealing an instability in de Sitter space due to semi-classical back reaction.

Findings

Tracing over unobservable states yields a thermal spectrum.

De Sitter space becomes unstable under back reaction.

Horizon size increases gradually, indicating relaxation of cosmic acceleration.

Abstract

We investigate back reaction in de Sitter space in an approach where only states that are observationally accessible are included in the density matrix. Using the Bunch-Davies vacuum as the initial condition we find for a conformal scalar field and a cosmological constant that tracing over the unobservable states beyond the cosmological horizon leads to a thermal spectrum of particles and that such a configuration is unstable under semi-classical back reaction. It is concluded that this prescription results in an instability of de Sitter space with a gradually increasing horizon size.