f(R) theories

TL;DR

f(R) theories are a class of modified gravity models that extend General Relativity, with applications in cosmology and gravity, and various methods to test their differences from Einstein's theory.

Contribution

This review summarizes the applications, observational distinctions, and extensions of f(R) theories in cosmology and gravity research.

Findings

f(R) theories can explain inflation and dark energy.

They can satisfy both cosmological and local gravity constraints.

Various observational methods can distinguish f(R) from General Relativity.

Abstract

Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.