Causality in Lovelock Theories of Gravity

Harvey Reall (Cambridge)

Lovelock theories of gravity (e.g. Einstein-Gauss-Bonnet) are an interesting alternative to General Relativity in higher dimensions. They have the unusual property that gravity can travel faster or slower than light so causality is not determined by the light cone of the metric. I will explain how causality is defined by characteristic hypersurfaces and discuss some examples in which these hypersurfaces can be determined. I will discuss problems with arguments asserting that faster than light propagation implies causality violation. In particular, I will show that small black holes in Einstein-Gauss-Bonnet theory cannot be boosted arbitrarily close to the speed of light, which prevents one from building a time machine in this theory.