A cyclic cosmological model based on the f({\rho}) modified theory of gravity

TL;DR

This paper proposes a cyclic cosmological model within an f(ρ) modified gravity framework, aiming to unify early inflation, late acceleration, dark matter, and dark energy while avoiding singularities and passing solar system tests.

Contribution

It introduces a specific f(ρ) gravity model that achieves non-singular, cyclic cosmology with unified dark matter and energy, simplifying equations compared to F(R) theories.

Findings

Achieves non-singular, cyclic cosmology with bounded curvature.

Unifies dark matter and dark energy in a single framework.

Simplifies mathematical treatment compared to F(R) gravity.

Abstract

We consider FLRW cosmological models for perfect fluid (with rho as the energy density) in the frame work of the f(rho) modified theory of gravity [V. N. Tunyak, Russ. Phys. J. 21, 1221 (1978); J. R. Ray, L. L. Smalley, Phys. Rev. D. 26, 2615 (1982) ]. This theory, with total Lagrangian R-f(rho), can be considered as a cousin of the F(R) theory of gravity with total Lagrangian F(R)-rho. We can pick proper function forms f(rho) to achieve, as the F(R) theory does, the following 4 specific goals, (1) producing a non-singular cosmological model (Ricci scalar and Ricci tensor curvature are bounded); (2) explaining the cosmic early inflation and late acceleration in a unified fashion; (3) passing the solar system tests; (4) unifying the dark matter with dark energy. In addition we also achieve goal number (5): unify the regular matter/energy with dark matter/energy in a seamless fashion. The mathematics is simplified because in the f(rho) theory the leading terms in Einstein's equations are linear in second order derivative of metric wrt coordinates but in the F(R) theory the leading terms are linear in fourth order derivative of metric wrt coordinates.