On multifluid perturbations in scalar-tensor cosmology

TL;DR

This paper investigates scalar-tensor cosmology perturbations in a multi-fluid universe using covariant methods, analyzing scalar and harmonic decompositions during different cosmic epochs with a focus on energy density fluctuations.

Contribution

It applies the 1+3 covariant approach to scalar-tensor theories for multi-fluid perturbations, including scalar and harmonic decompositions, and examines their behavior in different cosmological epochs.

Findings

Energy density fluctuations decrease with increasing redshift.

Fluctuation behavior varies with the power law index n.

Results depend on the epoch and scalar field parameters.

Abstract

In this paper the scalar-tensor theory is applied to the study of perturbations in a multi-fluid universe, using the 1+3 covariant approach. Both scalar and harmonic decompositions are instituted on the perturbation equations. In particular, as an application, we study perturbations on a background FRW cosmology consisting of both radiation and dust in the presence of a scalar field. We consider both radiation-dominated and dust-dominated epochs, respectively, and study the results. During the analysis, quasi-static approximation is instituted. It is observed that the fluctuations of the energy density decrease with increasing redshift, for different values of $n$ of a power law $R^{n}$ model