Dark Energy and Equation of State Oscillations with Collisional Matter Fluid in Exponential Modified Gravity

TL;DR

This paper investigates cosmological evolution in exponential $F(R)$ gravity with collisional matter, focusing on dark energy oscillations, matter perturbations, and the absence of phantom divide crossings, revealing distinctions between collisional and non-collisional matter effects.

Contribution

It introduces a curvature corrected exponential $F(R)$ gravity model with collisional matter, analyzing dark energy oscillations and matter perturbations, and highlights the absence of phantom divide crossings in this context.

Findings

Dark energy oscillations do not cross the phantom divide.

Collisional and non-collisional matter universes are distinguishable via matter perturbations.

Oscillations in the effective equation of state are absent near the matter era.

Abstract

We study some aspects of cosmological evolution in a universe described by a viable curvature corrected exponential $F(R)$ gravity model, in the presence of matter fluids consisting of collisional matter and radiation. Particularly, we express the Friedmann-Robertson-Walker equations of motion in terms of parameters that are appropriate for describing the dark energy oscillations and compare the dark energy density and the dark energy equation of state parameter corresponding to collisional and non-collisional matter. In addition to these, and owing to the fact that the cosmological evolution of collisional and non-collisional matter universes, when quantified in terms of the Hubble parameter and the effective equation of states parameters, is very much alike, we further scrutinize the cosmological evolution study by extending the analysis to the study of matter perturbations in the matter domination era. We quantify this analysis in terms of the growth factor of matter perturbations, in which case the resulting picture of the cosmological evolution is clear, since collisional and non-collisional universes can be clearly distinguished. Interestingly enough, since it is known that the oscillations of the effective equation of state parameter around the phantom divide are undesirable and unwanted in $F(R)$ gravities, when these are considered for redshifts near the matter domination era and before, in the curvature corrected exponential model with collisional matter which we study here there exist oscillations that never cross the phantom divide. Therefore, this rather unwanted feature of the effective equation of state parameter is also absent in the collisional matter filled universe.