Qualitative types of cosmological evolution in hydrodynamic models with barotropic equation of state

TL;DR

This paper provides a qualitative classification of all possible cosmological solutions in homogeneous isotropic universes filled with a perfect fluid obeying a barotropic equation of state, including singular, oscillating, and singularity-free scenarios.

Contribution

It offers a comprehensive classification of cosmological solutions with a general barotropic fluid, analyzing monotony, extendibility, and singularities, including multicomponent fluids.

Findings

Identified conditions for Big Rip and other singularities.

Classified oscillating and singularity-free solutions.

Extended analysis to multicomponent fluid models.

Abstract

We study solutions of the Friedmann equations in case of the homogeneous isotropic Universe filled with a perfect fluid. The main points concern the monotony properties of the solutions, the possibility to extend the solutions on all times and occurrence of singularities. We present a qualitative classification of all possible solutions in case of the general smooth barotropic equation of state of the fluid, provided the speed of sound is finite. The list of possible scenarios includes analogs of the "Big Rip" in the future and/or in the past as well as singularity free solutions and oscillating Universes. Extensions of the results to the multicomponent fluids are discussed.