Dynamics of classes of barotropic fluids in spatially curved FRW spacetimes

TL;DR

This paper analyzes the dynamical behavior of a broad class of barotropic fluids in curved FRW spacetimes, identifying critical points and invariant sets without assuming a cosmological constant, and compares specific EoS examples with prior studies.

Contribution

It introduces a general dynamical framework for barotropic fluids in curved FRW universes, including a new function $\Gamma$ for EoS characterization, and applies it to specific examples.

Findings

Identified critical points and invariant subsets in the dynamical system.

Developed a general method to analyze barotropic fluids without a cosmological constant.

Compared specific EoS examples with previous quadratic EoS studies.

Abstract

In this article we perform dynamical analysis of a broad class of barotropic fluids in the spatially curved Friedmann-Robertson-Walker (FRW) spacetime background without considering the cosmological constant. The first part of our study concerns the dynamics of a fluid with an unspecified barotropic equation of state (EoS) having as the only assumption the non-negativity of the fluid's energy density. After defining a new set of dimensionless variables and a new evolution parameter, we introduce the function $\Gamma$ that encodes the EoS. In this general setup several features of the system are identified: critical points, invariant subsets and the characteristics of the function $\Gamma$, along with their cosmological interpretations. The second part of our work provides two examples with specific $\Gamma$ functions. In the first example we provide a $\Gamma$ function and then we exhibit how it can be trimmed down to a specific class of EoS through physical arguments, while in the second example we discuss the quadratic EoS studied in Phys.Rev. D {\bf 74}, 023523 (2006) by comparing our approach with their analysis.