Dissipative Unified Dark Fluid Model

TL;DR

This paper introduces a dissipative unified dark fluid model combining adiabatic and bulk viscous components, analyzed through phase space and observational data, to explain universe evolution including dark energy and matter.

Contribution

It presents a novel unified dark fluid model with bulk viscosity, analyzed via phase space and observational constraints, capable of interpolating between dust and dark energy behaviors.

Findings

Model can interpolate between dust and dark energy equations of state.

Results show the model fits observational Hubble data well.

Estimated viscosity coefficient aligns with previous studies.

Abstract

We consider a unified dissipative dark fluid model. Our fluid contains an adiabatic part plus a bulk viscous one. The adiabatic part has the ability to asymptote between two power laws and so can interpolate between the dust and dark energy equations of state at early and late times. The dissipative part is a bulk viscous part with constant viscosity coefficient. The model is analyzed using the phase space methodology which helps to understand the dynamical behavior of the model in a robust manner without reference to the system solution. The parameters of the model are constrained through its asymptotic behavior and also through many observational constraints. We solve the Hubble parameter equation using numerical methods and results are plotted against the newest set of Hubble data. The model is tested using the $Om(z)$ test which shows that this model although is a quintessence-like model, it slides through the phantom barrier. We study the model expectations for the evolution of the universe by studying the evolution of the deceleration parameter, the density of the universe, the effective equation of state parameter of the model and of its underlying dark energy package. We estimate the value of the present day viscosity coefficient of the cosmic fluid as $8 \times 10^6 Pa.s$, which agrees with the work of many authors, e.g., Velten and Schwartz [26], Wang and Meng [27], and Sasidharan and Mathew [29]. We argue that this model is able to explain the behavior of the universe evolution.