Lovelock theory of gravity

Summary

Lovelock theory is the most general local metric theory of gravity in $D$ dimensions with second-order field equations. Its Lagrangian is a sum of terms built from powers of the Riemann curvature tensor, each a dimensional continuation of an Euler density. In four dimensions it reduces to general relativity with a cosmological constant, as Lovelock's theorem says. In higher dimensions it allows new terms, the first of which is the Gauss–Bonnet term.