Dynamics and chaos in the unified scalar field Cosmology

TL;DR

This paper investigates the chaotic dynamics of closed scalar field cosmological models within the Unified Dark Matter scenario, highlighting the role of spatial curvature and comparing model predictions with observational data.

Contribution

It provides a combined theoretical and numerical analysis showing chaos depends on curvature and demonstrates the model's consistency with observational Hubble parameter data.

Findings

Chaos is linked to positive spatial curvature.

Flat models do not exhibit chaos.

The model aligns well with observational data.

Abstract

We study the dynamics of the closed scalar field FRW cosmological models in the framework of the so called Unified Dark Matter (UDM) scenario. Performing a theoretical as well as a numerical analysis we find that there is a strong indication of chaos in agreement with previous studies. We find that a positive value of the spatial curvature is essential for the appearance of chaoticity, though the Lyapunov number seems to be independent of the curvature value. Models that are close to flat exhibit a chaotic behavior after a long time while pure flat models do not exhibit any chaos. Moreover, we find that some of the semiflat models in the UDM scenario exhibit similar dynamical behavior with the Lambda cosmology despite their chaoticity. Finally, we compare the measured evolution of the Hubble parameter derived from the differential ages of passively evolving galaxies with that expected in the semiflat unified scalar field cosmology. Based on a specific set of initial conditions we find that the UDM scalar field model matches well the observational data.