Cosmological evolution in exponential gravity

TL;DR

This paper investigates the cosmological evolution in exponential gravity models, demonstrating late-time acceleration, dark energy behavior, and increasing horizon entropy, contributing to the understanding of modified gravity theories in cosmology.

Contribution

It provides a detailed analysis of exponential gravity $f(R)$ models, showing their viability for explaining cosmic acceleration and dark energy phenomena.

Findings

Late-time cosmic acceleration can be achieved.

Dark energy equation of state can cross the phantom divide.

Cosmological horizon entropy increases over time.

Abstract

We explore the cosmological evolution in the exponential gravity $f(R)=R +c_1 (1-e^{- c_2 R})$ ($c_{1, 2} = \mathrm{constant}$). We summarize various viability conditions and explicitly demonstrate that the late-time cosmic acceleration following the matter-dominated stage can be realized. We also study the equation of state for dark energy and confirm that the crossing of the phantom divide from the phantom phase to the non-phantom (quintessence) one can occur. Furthermore, we illustrate that the cosmological horizon entropy globally increases with time.