A model of the late universe with viscous Zel'ldovich fluid and decaying vacuum

TL;DR

This paper proposes a cosmological model with viscous Zel'dovich fluid and decaying vacuum energy, which successfully predicts the universe's late acceleration, age, and a stable de Sitter end phase.

Contribution

It introduces a new flat universe model combining viscous stiff fluid and decaying vacuum energy, addressing previous age prediction issues and demonstrating stability of the de Sitter phase.

Findings

Predicts a reasonable age for the universe

Shows a stable de Sitter end phase

Aligns with observed late-time acceleration

Abstract

Many have speculated about the presence of a stiff fluid in very early stage of the universe. Such a stiff fluid was first introduced by Zel'dovich. Recently the late acceleration of the universe was studied by taking bulk viscous stiff fluid as the dominant cosmic component, but the age predicted by such a model is less than the observed value. We consider a flat universe with viscous stiff fluid and decaying vacuum energy as the cosmic components and found that the model predicts a reasonable background evolution of the universe with de Sitter epoch as end phase of expansion. More over the model also predicts a reasonable value for the age of the present universe. We also perform a dynamical system analysis of the model and found that the end de Sitter phase predicted by the model is stable.