Scalar perturbation of the viscosity dark fluid cosmological model

TL;DR

This paper studies scalar perturbations in a unified dark fluid model with viscosity, deriving exact solutions and comparing its behavior to the standard $\\Lambda$CDM model, revealing similar early universe behavior but differences at late times.

Contribution

It provides an exact solution for scalar perturbations in a viscous dark fluid model and compares its evolution to the standard cosmological model.

Findings

Perturbation quantities can be exactly obtained in the future universe.

The model's gravitational potential and density perturbations behave similarly to the standard model.

Significant differences appear in late universe perturbation values.

Abstract

A general equation of state is used to model unified dark matter and dark energy (dark fluid), and it has been proved that this model is equivalent to a single fluid with time-dependent bulk viscosity. In this paper, we investigate scalar perturbation of this viscosity dark fluid model. For particular parameter selection, we find that perturbation quantity can be obtained exactly in the future universe. We numerically solve the perturbation evolution equations, and compare the results with those of $\Lambda$CDM model. Gravitational potential and the density perturbation of the model studied here have the similar behavior with the standard model, though there exists significant value differences in the late universe.