The Hubble parameter in the early universe with viscous QCD matter and finite cosmological constant

TL;DR

This paper models the early universe's expansion considering viscous QCD matter and a finite cosmological constant, revealing prolonged Hubble parameter evolution and a singularity at zero cosmic time.

Contribution

It introduces a new approach combining viscous QCD matter and dark energy effects to analyze early universe dynamics, extending previous idealized models.

Findings

Evidence of a singularity at zero cosmic time due to dark energy.

Extended duration of Hubble parameter evolution with viscosity and cosmological constant.

Approximate solutions derived using recent QCD and heavy-ion collision data.

Abstract

The evolution of a flat, isotropic and homogeneous universe is studied. The background geometry in the early phases of the universe is conjectured to be filled with causal bulk viscous cosmological fluid and dark energy. The energy density relations obtained from the assumption of covariant conservation of energy-momentum tensor of the background matter in the early universe are used to derive the basic equation for the Hubble parameter $H$. The viscous properties described by ultra-relativistic equations of state and bulk viscosity taken from recent heavy-ion collisions and lattice QCD calculations have been utilized to give an approximate solution of the field equations. The cosmological constant is conjectured to be related to the energy density of the vacuum. In this treatment, there is a clear evidence for singularity at vanishing cosmic time $t$ indicating the dominant contribution from the dark energy. The time evolution of $H$ seems to last for much longer time than the ideal case, where both cosmological constant and viscosity coefficient are entirely vanishing.