Singular $F(R)$ Cosmology Unifying Early and Late-time Acceleration with Matter and Radiation Domination Era

TL;DR

This paper develops $F(R)$ gravity models that unify early inflation, radiation, matter, and late-time acceleration eras, incorporating Type IV singularities to match observational data and describe the universe's evolution comprehensively.

Contribution

The paper introduces two novel $F(R)$ gravity models that unify all major cosmological epochs with specific singularities, extending previous models and aligning with observational constraints.

Findings

Models produce nearly scale-invariant power spectrum

Scalar-to-tensor ratio compatible with observations

Deceleration-acceleration transition influenced by Type IV singularity

Abstract

We present some cosmological models which unify the late and early-time acceleration eras with the radiation and the matter domination era, and we realize the cosmological models by using the theoretical framework of $F(R)$ gravity. Particularly, the first model unifies the late and early-time acceleration with the matter domination era, and the second model unifies all the evolution eras of our Universe. The two models are described in the same way at early and late times, and only the intermediate stages of the evolution have some differences. Each cosmological model contains two Type IV singularities which are chosen to occur one at the end of the inflationary era and one at the end of the matter domination era. The cosmological models at early times are approximately identical to the $R^2$ inflation model, so these describe a slow-roll inflationary era which ends when the slow-roll parameters become of order one. The inflationary era is followed by the radiation era and after that the matter domination era follows, which lasts until the second Type IV singularity, and then the late-time acceleration era follows. The models produce a nearly scale invariant power spectrum of primordial curvature perturbations and a scalar-to-tensor ratio which are compatible with the most recent observational data and it seems that the deceleration acceleration transition is crucially affected by the presence of the second Type IV singularity which occurs at the end of the matter domination era. We perform an analysis of the Hubble horizon evolution, and in addition, we investigate which $F(R)$ gravity can successfully realize each of the four cosmological epochs.