A PAge-like Unified Dark Fluid Model

TL;DR

This paper introduces a PAge-like Unified Dark Fluid (PUDF) model that unifies dark matter and dark energy, fitting cosmological data well but still favoring the standard Lambda-CDM model based on Bayesian evidence.

Contribution

The paper proposes a novel PUDF model based on the PAge approximation, providing an alternative unified dark fluid framework consistent with key cosmological observations.

Findings

PUDF model effectively describes large-scale structure and cosmic acceleration.

Data analysis favors Lambda-CDM over PUDF based on Bayesian evidence.

PUDF fits observational data well despite being less favored statistically.

Abstract

The unified dark fluid model unifies dark matter and dark energy into a single component, providing an alternative and more concise framework for interpreting cosmological observations. We introduce a PAge-like Unified Dark Fluid (PUDF) model based on the PAge approximation (Huang 2020), which is parameterized by the age of the universe and an $\eta$ parameter indicating the deviation from Einstein-De Sitter Universe. The PUDF model shares many similar features of the standard Lambda cold dark matter ($\Lambda$CDM) model and can effectively describe the large-scale structure formation and late-time cosmic acceleration. We constrain the PUDF model with the Planck 2018 cosmic microwave background anisotropies, baryon acoustic oscillation measurements including those from the most recent DESI 2024, the Pantheon+ sample of Type Ia supernovae, and the Cosmic Chronometers compilation. Although the PUDF performs well in fitting all the cosmological datasets, the joint analysis of the data still favors the $\Lambda$CDM model over the PUDF model, according to the Bayesian evidence of model comparison.