Analysing dissipative effects in the $\Lambda$CDM model

TL;DR

This paper investigates the impact of viscous dark matter within the $\\Lambda$CDM model using Israel-Stewart theory, revealing new solutions and constraints that could influence cosmological understanding.

Contribution

It introduces a viscous dark matter component via Israel-Stewart theory into the $\\Lambda$CDM model, deriving new solutions and analyzing thermodynamic conditions.

Findings

Wider range of de Sitter solutions compared to standard $\\Lambda$CDM.

Conditions for near thermodynamical equilibrium are established.

Constraints on the model are suggested using Supernovae Ia data.

Abstract

In the present paper, the effects of viscous dark matter are analysed within the $\Lambda$CDM model. Here we consider bulk viscosity through the Israel-Stewart theory approach, leading to an effective pressure term in the continuity equation that accomplishes for the dissipative effects of the dark matter fluid. Then, the corresponding equation for viscosity is solved and a general equation for the Hubble parameter is obtained with the presence of a cosmological constant. The existence of de Sitter solutions is discussed, where a wider range of solutions is found in comparison to the $\Lambda$CDM model. Also the conditions for the near thermodynamical equilibrium of the fluid is analysed. Finally, a qualitative analysis provides some constraints on the model by using Supernovae Ia data which reveals the possible importance of causal thermodynamics in cosmology.