Bianchi I cosmology in the presence of a causally regularized viscous fluid

TL;DR

This paper investigates how a causally regularized viscous fluid influences the early universe's dynamics in Bianchi I cosmology, revealing matter creation, singularity structure, and potential inflationary behavior.

Contribution

It introduces a causally regularized viscous fluid model in Bianchi I cosmology and explores its effects on singularity, matter creation, and inflation.

Findings

Viscous effects induce matter creation from a singularity.

In the isotropic limit, viscosity modifies the universe's power-law behavior.

Strong viscous effects can lead to inflation and entropy production.

Abstract

We analyze the dynamics of a Bianchi I cosmology in the presence of a viscous fluid, causally regularized according to the Lichnerowicz approach. We show how the effect induced by shear viscosity is still able to produce a matter creation phenomenon, meaning that also in the regularized theory we address, the Universe is emerging from a singularity with a vanishing energy density value. We discuss the structure of the singularity in the isotropic limit, when bulk viscosity is the only retained contribution. We see that, as far as viscosity is not a dominant effect, the dynamics of the isotropic Universe possesses the usual inviscid power-law behavior but in correspondence of aneffective equation of state, depending on the bulk viscosity coefficient. Finally, we show that, in the limit of a strong non-thermodynamical equilibrium of the Universe mimicked by a dominant contribution of the effective viscous pressure, a power-law inflation behavior of the Universe appears, the cosmological horizons are removed and a significant amount of entropy is produced.