Born-Infeld-Horava gravity

We define various Born-Infeld gravity theories in 3+1 dimensions which reduce to Horava's model at the quadratic level in small curvature expansion. In their exact forms, our actions provide z->(infinity) extensions of Horava's gravity, but when small curvature expansion is used, they reproduce finite z models, including some half-integer ones.Comment: 7 pages, typo corrected, matches the published versio

Gravity Waves in Three Dimensions

We find the explicit forms of the anti-de Sitter plane, anti-de Sitter spherical, and pp waves that solve both the linearized and exact field equations of the most general higher derivative gravity theory in three dimensions. As a sub-class, we work out the six derivative theory and the critical version of it where the masses of the two spin-2 excitations vanish and the spin-0 excitations decouple.Comment: 14 pages, matches the published versio

AdS-Wave Solutions of f(Riemann) Theories

We show that the recently found AdS-plane and AdS-spherical wave solutions of quadratic curvature gravity also solve the most general higher derivative theory in D-dimensions. More generally, we show that the field equations of such theories reduce to an equation linear in the Ricci tensor for Kerr-Schild spacetimes having type-N Weyl and traceless Ricci tensors.Comment: 4 pages, solutions are extended for generic f(Riemann) theories that include arbitrary powers of the curvatur

Kerr-Schild--Kundt Metrics are Universal

We define (non-Einsteinian) universal metrics as the metrics that solve the source-free covariant field equations of generic gravity theories. Here, extending the rather scarce family of universal metrics known in the literature, we show that the Kerr-Schild--Kundt class of metrics are universal. Besides being interesting on their own, these metrics can provide consistent backgrounds for quantum field theory at extremely high energies.Comment: 31 pages, To appear in the Journal of Classical and Quantum Gravit