On multifluid perturbations in scalar–tensor cosmology

Abstract

In this paper, the scalar–tensor theory is applied to the study of perturbations in a multifluid universe, using the [Formula: see text] covariant approach. Both scalar and harmonic decompositions are instituted on the perturbation equations. In particular, as an application, we study perturbations on a background Friedmann-Robertson-Walker (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 [Formula: see text] of a power-law [Formula: see text] model.