Interacting cosmic fluids in power-law Friedmann-Robertson-Walker cosmological models

TL;DR

This paper explores power-law Friedmann-Robertson-Walker cosmological models with two interacting perfect fluids, showing how interactions can lead to accelerated expansion and mimic single-fluid solutions, unlike non-interacting cases.

Contribution

It provides a detailed analysis of interacting fluid scenarios in power-law FRW models, revealing conditions for acceleration and equivalence to single-fluid models.

Findings

Interacting fluids can produce accelerated expansion in flat FRW models.

Power-law solutions with interacting fluids can mimic single-fluid cosmologies.

Non-interacting fluids do not generally admit power-law solutions with similar properties.

Abstract

We provide a detailed description for power--law scaling Friedmann-Robertson-Walker cosmological scenarios dominated by two interacting perfect fluid components during the expansion. As a consequence of the mutual interaction between the two fluids, neither component is conserved separately and the energy densities are proportional to $1/t^{2}$. It is shown that in flat FRW cosmological models there can exist interacting superpositions of two perfect fluids (each of them having a positive energy density) which accelerate the expansion of the universe. In this family there also exist flat power law cosmological scenarios where one of the fluids may have a ``cosmological constant" or "vacuum energy" equation of state ($p =-\rho$) interacting with the other component; this scenario exactly mimics the behavior of the standard flat Friedmann solution for a single fluid with a barotropic equation of state. These possibilities of combining interacting perfect fluids do not exist for the non-interacting mixtures of two perfect cosmic fluids, where the general solution for the scale factor is not described by power--law expressions and has a more complicated behavior. In this study is considered also the associated single fluid model interpretation for the interaction between two fluids.