Dark matter perturbations and viscosity: A causal approach

Abstract

The inclusion of dissipative effects in cosmic fluids modifies their clustering properties and could have observable effects on the formation of large scale structures. We analyse the evolution of density perturbations of cold dark matter endowed with causal bulk viscosity. The perturbative analysis is carried out in the Newtonian approximation and the bulk viscosity is described by the causal Israel-Stewart (IS) theory. In contrast to the non-causal Eckart theory, we obtain a third order evolution equation for the density contrast that depends on three free parameters. For certain parameter values, the density contrast and growth factor in IS mimic their behaviour in ΛCDM when z ≥ 1. Interestingly, and contrary to intuition, certain sets of parameters lead to an increase of the clustering.

Jeans instability in a universe with dissipation

“…Probably, our line of work is similar to the one employed by Acquaviva et al because they worked within the framework of Newtonian cosmology and they considered the presence of dissipative effects by including a bulk viscosity term which corrects the standard pressure term of Euler equation. Moreover, they added a transport equation for Π v based on the Israel and Steward causal theory [28]. This is equivalent to promote Π v to the rank of another field of the theory which must be determined dynamically.…”

Bulk viscosity, interaction and the viability of phantom solutions

“…(3) corresponds to the bulk viscous pressure of the dark matter fluid, with ζ the bulk viscous coefficient. In the literature [10,17,18,25,28,[35][36][37][38], the usual ansatz 3 for the bulk viscous coefficient ζ is…”

“…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.…”

Mimetic Dark Matter in Pseudo-Complex General Relativity

“…7 In addition, bulk viscosity has another important feature for cosmology: it can generate an accelerated expansion era without invoking dark energy. 8 There are recent works that treated viscous dark matter in the domain of General relativity extesions. In Ref.…”