Non-singular modified gravity unifying inflation with late-time acceleration and universality of viscous ratio bound in F(R) theory

TL;DR

This paper reviews F(R)-gravity theories, focusing on their cosmological solutions that unify early inflation with late-time acceleration, and discusses the universality of viscous ratio bounds in higher-dimensional models.

Contribution

It introduces new non-singular F(R)-gravity models unifying inflation and dark energy, and explores the universal viscous ratio bound in five-dimensional F(R)-gravity.

Findings

New non-singular F(R)-gravity models unify inflation with dark energy.

Finite-time singularities can be avoided with R^2-term inclusion.

Universal viscous ratio bound is derived in five-dimensional F(R)-gravity.

Abstract

The review of basic cosmological properties of four-dimensional F(R)-gravity, including FRW equations of motion and its accelerating solutions, generalized fluid and scalar-tensor representation of the theory is done. Cosmological reconstruction equation is written and conditions for stability of cosmological solution are discussed. The overview of realistic F(R)-models unifying inflation with dark energy epoch is made. The avoidance of finite-time future singularities in such theories via the introduction of R^2-term is studied. New realistic non-singular F(R)-gravity unifying early-time inflation with late-time acceleration is presented. The exit from inflationary era in such model may be caused by the gravitational scenario. It is demonstrated that five-dimensional F(R)-gravity considered as non-perturbative stringy effective action leads to universal relation for viscous bound ratio.