Cosmological models with fluid matter undergoing velocity diffusion

TL;DR

This paper introduces a novel cosmological fluid model with velocity diffusion in general relativity, incorporating a scalar field to account for energy gain, which leads to new insights into accelerated cosmic expansion.

Contribution

It presents a new fluid matter model with diffusion and a scalar field in Einstein's equations, offering a fresh mechanism for cosmic acceleration.

Findings

Diffusion modifies the global dynamics of cosmological models.

The scalar field compensates for energy gained by diffusing particles.

Diffusion introduces qualitative changes to standard cosmological behaviors.

Abstract

A new type of fluid matter model in general relativity is introduced, in which the fluid particles are subject to velocity diffusion without friction. In order to compensate for the energy gained by the fluid particles due to diffusion, a cosmological scalar field term is added to the left hand side of the Einstein equations. This hypothesis promotes diffusion to a new mechanism for accelerated expansion in cosmology. It is shown that diffusion alters not only quantitatively, but also qualitatively the global dynamical properties of the standard cosmological models.