Observational constraints on phenomenological emergent dark energy and barotropic dark matter characterized by a constant equation of state parameter

TL;DR

This study introduces a cosmological model where dark matter has a constant equation of state and dark energy is emergent, with observational constraints showing some tensions but overall favoring the new model over PEDE.

Contribution

The paper proposes a novel dark matter and dark energy model with observational constraints, contrasting it with the existing PEDE model and analyzing its viability.

Findings

Preference for positive dark matter equation of state at 68% confidence.

Reduction of the S8 tension from 2.3σ to 0.4σ.

Bayesian evidence favors the new model over PEDE.

Abstract

We propose a new cosmological model that considers dark matter as a barotropic fluid with a constant equation of state parameter and interprets dark energy as the phenomenological emergent dark energy rather than a cosmological constant. This proposal is based on extensive research on the extended properties of dark matter in the context of a cosmological constant and the intriguing findings that have emerged from our exploration of dark matter properties within the context of PEDE in our previous studies. We then place constraints on this model in light of the Planck 2018 Cosmic Microwave Background (CMB) anisotropies, baryon acoustic oscillation (BAO) measurements, the Pantheon compilation of Type Ia supernovae, a prior on $H_0$ that based on the latest local measurement by Riess et al., and the combination of KiDS and the VISTA Kilo-Degree Infrared Galaxy Survey (KiDS+VIKING-450). The results indicate a preference for a positive dark matter equation of state parameter at 68\% confidence level for CMB+BAO, CMB+BAO+Pantheon and CMB+BAO+Pantheon+$H_0$ datasets. Furthermore, the Hubble tension between all of the datasets we used with R22 is very close to those of the PEDE, and the $S_8$ tension between Planck 2018 and KiDS+VIKING-450 is reduced from 2.3$\sigma$ in the PEDE model to 0.4$\sigma$ in the new model. However, Bayesian evidence indicates that PEDE favors our new model with very strong evidence from all the datasets considered in this study. Consequently, we conclude that the PEDE+$w_{\rm dm}$ model is not a viable alternative to the PEDE model.