Linking little rip cosmologies with regular early universes

TL;DR

This paper introduces regular Little Rip cosmologies with a generalized equation of state that avoids initial and future singularities, providing a unified model for emergent universes and late-time acceleration.

Contribution

It demonstrates that GEoS fluids can produce non-singular universes that encompass both early emergent phases and late-time Little Rip behavior, linking past and future cosmic regimes.

Findings

Regular universes free of initial singularity

Conditions linking Little Rip and emergent universe scenarios

Models avoiding Big Bang and Big Rip singularities

Abstract

Cosmological fluids with a Generalized Equation of State (GEoS) are here considered, whose corresponding EoS parameter $\omega$ describes a fluid with phantom behavior, namely $\omega<-1$, but leading to universes free of singularities at any past or future, finite time. Thus avoiding, in particular, the Big Bang and the Big Rip singularities, the last one considered to be typical in phantom fluid models. More specifically, such GEoS fluid cosmologies lead to regular Little Rip universes. A remarkable new property of these solutions is proven here, namely that they avoid the initial singularity at early times; therefore, they are able to describe emergent universes. Solutions of this kind had been studied previously, but only either as late time or as early time solutions; never as solutions covering both epochs simultaneously. Appropriate conditions are proposed here that relate the Little Rip cosmologies with the initial regular universe, for the future and past regimes, respectively. This is done by taking as starting point the conditions under which a given scale factor corresponds to a Little Rip universe.