Stationary Killing horizons and conformal entropy in higher order gravity theories Available to Purchase

Boundary conditions, that follow from regularity of invariants of Riemann tensor on the horizon, can be used to derive microscopic entropy formula, based on Virasoro approach, for Lagrangians with arbitrary dependence on Riemann tensor. An example of a Lagrangian with derivatives of Riemann tensor suggests that boundary conditions can be obtained from regularity of invariants involving derivatives of Riemann tensor and that leads to new properties of metric functions near horizon.