Effective Phantom Divide Crossing with Standard and Negative Quintessence

TL;DR

This paper proposes that the observed peak in dark energy density around redshift 0.4-0.5 can be explained by a combination of standard and negative quintessence, avoiding the need for a true phantom divide crossing.

Contribution

It introduces a model with negative quintessence to interpret dark energy data, showing it can fit observations better than the standard Lambda-CDM model.

Findings

Negative quintessence explains the DE peak without crossing the phantom divide.

Model preferred over Lambda-CDM at 3.26 sigma confidence level.

Negative quintessence remains relevant at intermediate redshifts.

Abstract

Cosmic microwave background data from the {\it Planck} satellite, combined with baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument and Type Ia supernovae from various samples, provide hints of dynamical dark energy (DE). These results indicate a peak in the DE density around $z\sim 0.4-0.5$, with the highest significance observed when using the supernovae from the Dark Energy Survey. In this {\it Letter}, we show that this peak does not necessarily imply a true crossing of the phantom divide if the measured effective DE is not a single component, but a combination of standard and negative quintessence. The latter is characterized by negative energy density and positive pressure, both decreasing in absolute value and tending to 0 in the future. For appropriate values of the parameters, negative quintessence is relevant at intermediate redshifts and becomes subdominant in front of standard quintessence around $z\sim 0.4-0.5$, giving rise to the aforementioned peak in the DE density. We find that our model is preferred over $\Lambda$CDM at a $3.26\sigma$ CL, which is comparable to the level of exclusion found with the Chevallier-Polarski-Linder parametrization. Our analysis leaves open the possibility of negative quintessence and other exotic fields existing in the low-energy universe, potentially playing a significant role in cosmic dynamics.