Einstein–Gauss–Bonnet gravity

Summary

Einstein–Gauss–Bonnet gravity is general relativity with the Gauss–Bonnet term $R^2 - 4R_{ab}R^{ab} + R_{abcd}R^{abcd}$ added to the action. It is the simplest Lovelock theory beyond general relativity and has second-order field equations. The added term changes the field equations only in dimension five or more. In four dimensions its integral is a topological invariant, by the Chern–Gauss–Bonnet theorem. It appears in the low-energy limit of some string theories and gives new black hole solutions in higher dimensions.