Decoherence Can Relax Cosmic Acceleration

TL;DR

This paper demonstrates that quantum decoherence of a scalar field can lead to the decay of vacuum energy, causing the universe's accelerated expansion to slow down and potentially cease.

Contribution

It introduces a semi-classical model including decoherence effects, showing how quantum-to-classical transition influences cosmic acceleration.

Findings

Decoherence causes the Hubble rate to decrease over time.

Vacuum energy can decay due to quantum effects.

Universe's curvature can approach zero as a result.

Abstract

In this work we investigate the semi-classical backreaction for a quantised conformal scalar field and classical vacuum energy. In contrast to the usual approximation of a closed system, our analysis includes an environmental sector such that a quantum-to-classical transition can take place. We show that when the system decoheres into a mixed state with particle number as the classical observable de Sitter space is destabilized, which is observable as a gradually decreasing Hubble rate. In particular we show that at late times this mechanism can drive the curvature of the Universe to zero and has an interpretation as the decay of the vacuum energy demonstrating that quantum effects can be relevant for the fate of the Universe.