Dark Energy: Vacuum Fluctuations, the Effective Phantom Phase, and Holography

TL;DR

This paper explores models of dark energy that mimic phantom behavior without exotic matter, using vacuum fluctuations and holography, and discusses quantum effects preventing future singularities.

Contribution

It introduces two novel dark energy models—decaying vacuum cosmology with vacuum fluctuations and a holographic model with an infrared cutoff—that produce effective phantom phases.

Findings

Phantom behavior can emerge from vacuum fluctuations without exotic matter.

Quantum effects can prevent Big Rip singularities in holographic models.

The models provide alternative explanations for dark energy phenomena.

Abstract

We aim at the construction of dark energy models without exotic matter but with a phantom-like equation of state (an effective phantom phase). The first model we consider is decaying vacuum cosmology where the fluctuations of the vacuum are taken into account. In this case, the phantom cosmology (with an effective, observational $\omega$ being less than -1) emerges even for the case of a real dark energy with a physical equation of state parameter $\omega$ larger than -1. The second proposal is a generalized holographic model, which is produced by the presence of an infrared cutoff. It also leads to an effective phantom phase, which is not a transient one as in the first model. However, we show that quantum effects are able to prevent its evolution towards a Big Rip singularity.