Testing dissipative dark matter in causal thermodynamics

Abstract

In this paper we study the consistency of a cosmological model, described by a novel exact analytic solution of a universe filled with a dissipative dark matter fluid, in the framework of the causal Israel-Stewart theory, testing it by using Type Ia Supernovae data. The solution is obtained when we assume for the fluid a bulk viscous coefficient with the dependence ξ = ξ0ρ 1/2 , where ρ is the energy density of the fluid. It is further considered a relaxation time τ of the form ξ (ρ+p)τ = c 2 b , where c 2 b is the speed of bulk viscous perturbations, and a barotropic EoS p = (γ − 1) ρ. The constraints found for the parameters of the model allow to obtain exact solutions compatible with an accelerated expansion at late times, after the domination era of the viscous pressure and without the inclusion of a cosmological constant. Nevertheless, the fitted parameter values present drawbacks as a very large non-adiabatic contribution to the speed of sound, and some inconsistencies with the description of the dissipative dark matter as a fluid.

Unified dissipative dark matter model in a non linear Israel-Stewart theory

“…Finally, as found in Ref. [22], by considering Hubble parameter measurements data we obtained that the best fit of the parameters for the exact solution leads to some inconsistencies since the value of the ξ 0 parameter is large, this contradicts the near equilibrium condition and other important demands. Some comments regarding this point are in order:…”

“…However, as found in Ref. [22] the best fit for the parameter ξ 0 is considerably large, in this case ξ 0 = 4.25 × 10 13 and = 0.374; therefore the near equilibrium condition can not be satisfied. On the other hand, if we consider the extension of solution (9) to a non linear regime we obtain the following best fit for the parameters of the model: ξ 0 = 2.13×10 −2 , = 1.18×10 −5 and k = 266.31 3 .…”

“…In Ref. [22] some aspects of the solution (9) were studied. The Israel-Stewart model is based on the assumption that only small deviations from equilibrium are permitted.…”

“…( 2). However, by using Supernovae Type Ia data some drawbacks in the model were found, according to the analysis performed in [22]. In order to have late times cosmic expansion, the best fit of the parameters imdicates that ξ 0 1 together with ω = 0.…”

On the feasibility of truncated Israel–Stewart model in the context of late acceleration

“…Owing to the non-causal nature of the Eckart formalism, the bulk viscosity driven late acceleration has been analysed using the full causal Israel-Stewart theory [18,19,[38][39][40][41].…”