Phenomenology of $\Lambda$-CDM model: a possibility of accelerating Universe with positive pressure

TL;DR

This paper explores a specific time-dependent $\Lambda$ model ($\dot \Lambda \\sim H^3$) within $\Lambda$-CDM cosmology, revealing that accelerated expansion can occur with positive pressure and negative energy density, and analyzing the sign change of the deceleration parameter.

Contribution

It introduces and analyzes the $\\dot \\Lambda \\sim H^3$ model, showing novel features like acceleration with positive pressure and negative energy density in $\\Lambda$-CDM cosmology.

Findings

Accelerated expansion occurs at negative energy density with positive pressure.

The model predicts a sign change in the deceleration parameter during cosmic evolution.

Derived expressions for the time-dependent equation of state parameter \\omega.

Abstract

Among various phenomenological $\Lambda$ models, a time-dependent model $\dot \Lambda\sim H^3$ is selected here to investigate the $\Lambda$-CDM cosmology. Using this model the expressions for the time-dependent equation of state parameter $\omega$ and other physical parameters are derived. It is shown that in $H^3$ model accelerated expansion of the Universe takes place at negative energy density, but with a positive pressure. It has also been possible to obtain the change of sign of the deceleration parameter $q$ during cosmic evolution.