Five-dimensional metric $f(R)$ gravity and the accelerated universe

TL;DR

This paper explores five-dimensional $f(R)$ gravity models, showing they can naturally explain the universe's current accelerated expansion and predict future recollapse, with constraints derived from observational data.

Contribution

It extends $f(R)$ gravity to five dimensions, analyzes specific models, and links their cosmological implications to observations and quantum cosmology predictions.

Findings

Constraints on model parameter m from current observations

Extra dimension dynamics can drive acceleration and deceleration phases

Predicted future recollapse of the universe within finite time

Abstract

The metric $f(R)$ theories of gravity are generalized to five-dimensional spacetimes. By assuming a hypersurface-orthogonal Killing vector field representing the compact fifth dimension, the five-dimensional theories are reduced to their four-dimensional formalism. Then we study the cosmology of a special class of $f(R)=\alpha R^m$ models in a spatially flat FRW spacetime. It is shown that the parameter $m$ can be constrained to a certain range by the current observed deceleration parameter, and its lower bound corresponds to the Kaluza-Klein theory. It turns out that both expansion and contraction of the extra dimension may prescribe the smooth transition from the deceleration era to the acceleration era in the recent past as well as an accelerated scenario for the present universe. Hence five-dimensional $f(R)$ gravity can naturally account for the present accelerated expansion of the universe. Moreover, the models predict a transition from acceleration to deceleration in the future, followed by a cosmic recollapse within finite time. This differs from the prediction of the five-dimensional Brans-Dicke theory but is in consistent with a recent prediction based on loop quantum cosmology.