Evolution of a Simple Inhomogeneous Anisotropic Cosmological Model with Diffusion

TL;DR

This paper models an inhomogeneous anisotropic universe with diffusion, analyzing how diffusion influences cosmic evolution, including delayed accelerated expansion, through numerical solutions of Einstein and diffusion equations for dust and radiation.

Contribution

It introduces a numerical analysis of a simple inhomogeneous anisotropic cosmology with diffusion, comparing dust and radiation cases and assessing diffusion's impact on cosmic evolution.

Findings

Diffusion delays the onset of accelerated expansion.

Dust and radiation models show different evolution patterns.

Diffusion effects are significant compared to diffusionless models.

Abstract

We investigate a simple inhomogeneous anisotropic cosmology (plane symmetric $G_2$ model) filled with a tilted perfect fluid undergoing velocity diffusion on a scalar field. Considered are two types of fluid: dust and radiation. We solve the system of Einstein field equations and diffusion equations numerically and demonstrate how the universe evolves towards its future asymptotic state. Also, typical time scales of characteristic processes are determined. The obtained results for dust- and radiation-filled cosmologies are compared to each other and to those in the diffusionless case, giving a hint on which effects can be the result of including diffusion in more complicated models. For example, diffusion causes the accelerated expansion stage to arrive at later times.