World Scientific
Skip main navigation

Cookies Notification

We use cookies on this site to enhance your user experience. By continuing to browse the site, you consent to the use of our cookies. Learn More
×

System Upgrade on Tue, May 28th, 2024 at 2am (EDT)

Existing users will be able to log into the site and access content. However, E-commerce and registration of new users may not be available for up to 12 hours.
For online purchase, please visit us again. Contact us at customercare@wspc.com for any enquiries.

Dark energy density and Israel–Stewart (IS) bulk viscosity model

    https://doi.org/10.1142/S021988782350086XCited by:0 (Source: Crossref)

    In this paper, we investigate the thermodynamics of a dark energy bulk viscosity model as a cosmic fluid. In this regard, the two theories of Eckart and Israel–Stewart (IS) are the bases of our work. Therefore, we first investigate the thermodynamics of cosmic fluids in the dark energy bulk viscosity model and the general relationships. Then, we express the thermodynamic relationships of Eckart’s theory. Due to the basic equations of Eckart’s theory and Friedmann’s equations, we consider two states, one is p=ρ (standard) and the other is pρ (non-standard). In the standard state, we define the pressure (p), energy density (ρ) and bulk viscosity coefficient (ξ) of the cosmic fluid in terms of cosmic time and we obtain its relations. We also mention that in this standard state, because of p=ρ, the value of a(t) is zero, so a(t) is not defined in this state. But in the non-standard case (pρ), the bulk viscosity coefficient (ξ) is zero and only the scale factor, pressure and energy density of the cosmic fluid are defined. We also consider two states of constant and variable bulk viscosity coefficients and obtain three Hubble constant parameters and scale factor in terms of cosmic time, and energy density in terms of scale factor. In the state of variable bulk viscosity coefficient, we consider the viscosity coefficient as the power law from energy density (ξ=αρs), which is α>0 and a constant. Following this, we discuss about the dissipative effects of cosmic fluids and examine the effects of energy density for dark energy in the IS theory. The results are comprehensively presented in Tables 1 and 2. Also, according to observational constraints, the results of the likelihood analysis for the IS viscous model are summarized in Table 3.

    PACS: 04.50.kd, 95.36.+x