f(R) gravity

Summary

$f(R)$ gravity is a family of alternatives to general relativity. In it the scalar curvature $R$ in the Einstein–Hilbert action is replaced by a function $f(R)$. The choice $f(R) = R - 2\Lambda$ gives general relativity with a cosmological constant. Other choices have been used to model cosmic inflation and the accelerated expansion of the universe without a cosmological constant.