Dark energy and equation of state oscillations with collisional matter fluid in exponential modified gravity

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 FriedmannRobertson-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 noncollisional 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.

Mimetic Gravity: A Review of Recent Developments and Applications to Cosmology and Astrophysics

“…Namely, that of dark energy oscillations [395] (see also e.g. [396][397][398][399]). The degree of freedom associated to the modification of GR (that is, dF (R)/dR) leads to high frequency oscillations of the dark energy around the line of the phantom divide during matter era.…”

A spherically symmetric null tetrads in non-minimal torsion-matter coupling extension of f(T) gravity

“…Also there are other modified gravity theories namely scalar tensor theory, Brane world scenario, f (G), f (R, G) and f (R) gravity theories, where R is the Ricci scalar, G = R μνρλ R μνρλ − R μν R μν + R 2 is the Gauss Bonnet invariant term and R μνρλ and R μν are the usual Riemann curvature tensor and Ricci tensor respectively. These modified theories (Sotiriou and Faraoni 2010;Nojiri and Odintsov 2003Capozziello 2002;Starobinsky 1980;Kerner 1982;Barrow and Ottewi 1983;Faraoni 2006;Schmidt 2007;Mitra et al 2014;Carroll et al 2004;Capozziello et al 2006;Nojiri et al 2009;Oikonomou et al 2015) are considered as gravitational alternatives for DE and may serve as dark matter (Sobouti 2007).…”

Unification of constant-roll inflation and dark energy with logarithmic R2-corrected and exponential F(R) gravity

“…where Λ = 7.93m 2 ,γ = 1/1000, m = 1.57 × 10 −67 eV, b is an arbitrary parameter [43,44,56] and n is a positive real parameter. This model has quite appealing inflationary dynamics in the context of constant-roll inflation, as we now evince.…”

“…Actually, by solving the differential equation (III.12) numerically we will be able to find how the dark energy oscillations behave at late-times, so for small redshifts. For our numerical analysis we shall use the following initial conditions [43,44,[54][55][56],…”