Exploring non-linear cosmological matter diffusion coefficients

TL;DR

This paper investigates how different phenomenological models of the diffusion coefficient affect cosmological background solutions within general relativity, considering various dependencies on universe expansion parameters.

Contribution

It introduces a study of non-linear diffusion coefficients in cosmology, exploring their effects on universe evolution with phenomenological dependencies.

Findings

Diffusion coefficient models influence cosmological dynamics.

Dependence on scale factor and matter density alters expansion behavior.

Results suggest new ways to incorporate diffusion in cosmological models.

Abstract

Since microscopic velocity diffusion can be incorporated into general relativity in a consistent way, we study cosmological background solutions when the diffusion phenomena takes place in an expanding universe. Our focus here relies on the nature of the diffusion coefficient $\sigma$ which measures the magnitude of such transport phenomena. We test dynamics where $\sigma$ has a phenomenological dependence on the scale factor, the matter density, the dark energy and the expansion rate.