Nariai metric is the first example of the singularity free model

TL;DR

The paper highlights that the Nariai metric is the first known example of a singularity-free, expanding perfect fluid cosmological model that satisfies the weak energy condition, representing a conformally non-flat Einstein space.

Contribution

It identifies the Nariai metric as the first singularity-free expanding perfect fluid model satisfying the weak energy condition.

Findings

Nariai metric is singularity-free and expanding.

It satisfies the weak energy condition ($ ho>0, ho+p=0$).

It is a conformally non-flat Einstein space.

Abstract

This is just to point out that the Nariai metric is the first example of the singularity free expanding perfect fluid cosmological model satisfying the weak energy condition, $\rho>0, \rho+p=0$. It is a conformally non-flat Einstein space.