Interacting viscous dark fluids

Abstract

We revise the conditions for the physical viability of a cosmological model in which dark matter has bulk viscosity and also interacts with dark energy. We have also included radiation and baryonic matter components; all matter components are represented by perfect fluids, except the dark matter, that is treated as an imperfect fluid. We impose upon the model the condition of a complete cosmological dynamics that results in an either null or negative bulk viscosity, but the latter also disagrees with the Local Second Law of Thermodynamics. The model is also compared with cosmological observations at different redshifts: type Ia supernova, the shift parameter of CMB, the acoustic peak of BAO, and the Hubble parameter H(z). In general, observations consistently point out to a negative value of the bulk viscous coefficient, and in overall the fitting procedure shows no preference for the model over the standard ΛCDM model. PACS numbers: 95.36.+x, 98.80.Es

Bulk viscosity, interaction and the viability of phantom solutions

“…This kind of interaction mechanism has shown to be compatible with the current data [31]. In the context of viscous fluids, the interaction between dark matter and dark energy was studied in [21]. It has been shown that, under the ansatz ζ j = ζ j (H ), low-redshift data favors a positive definite value of the bulk viscosity, whereas high-redshift data prefers a negative value of the bulk viscosity.…”

“…This ansatz avoids the degeneracy problem associated with the case when the bulk viscosity is taken as ζ j = ζ j (H ) [20]. However, in [22], the same scenario was studied, from the dynamical system point of view, finding that viscous phantom solutions with stable behavior are not allowed in the framework of complete cosmological dynamics [21,30]. In the present paper we work along these lines by including an interaction between the dark matter and the dark energy.…”

“…In the present work we are interested in extending the results obtained in [20,22] by taking into account an interaction term between dark energy and dark matter and, at the same time, extending the results in [21] by exploring a different functional form for the bulk viscosity. 2 The paper is organized as follows: in Sect.…”

“…This approach has been explored in the literature through the moda e-mail: yoelsy.leyva@uta.cl eling of bulk viscosity in ordinary matter fluids [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] in the context of Eckart [26] or linear [27] and non-linear [28,29] Israel-Stewart theories.…”

“…We focus our attention on a particular form for the interaction term between the dark matter and dark energy components. A detailed discussion as regards the viability of a complete cosmological dynamics [21,30] is provided. Important constraints on the bulk viscosity and interaction parameter are obtained.…”