Matter Growth in Imperfect Fluid Cosmology

Abstract

Extensions of Einstein's General Relativity (GR) can formally be given a GR structure in which additional geometric degrees of freedom are mapped on an effective energy-momentum tensor. The corresponding effective cosmic medium can then be modeled as an imperfect fluid within GR. The imperfect fluid structure allows us to include, on a phenomenological basis, anisotropic stresses and energy fluxes which are considered as potential signatures for deviations from the cosmological standard Λ-cold-dark-matter (ΛCDM) model. As an example, we consider the dynamics of a scalartensor extension of the standard model, the eΦΛCDM model. We constrain the magnitudes of anisotropic pressure and energy flux with the help of redshift-space distortion (RSD) data for the matter growth function f σ8.

Accelerating imperfect fluid

“…As the fluid given by (2.2) is anisotropic, we write down the general expression of T ab in terms of the anisotropic pressures π ab , for any v(x). We have [9] T ab = ρu a u b + ph ab + π ab + u a q b + u b q a ,…”

Post-Editorial of the Special Issue “Estate Quantistica Conference—Recent Developments in Gravity, Cosmology, and Mathematical Physics”

“…However, we face a profound lack of knowledge about their microscopic nature, leading to many approaches aiming to describe their dynamics. Winfried Zimdahl, Hermano Velten and William Algoner discuss how to implement the description of large scale cosmological structure formation adopting nonstandard cosmic fluids possessing intrinsic viscous properties [7]. This is a step beyond the standard dark matter description based on perfect relativistic fluids.…”