Exact solutions to quadratic gravity

Understand

Since all Einstein spacetimes are vacuum solutions to quadratic gravity in four dimensions, in this paper we study various aspects of non-Einstein vacuum solutions to this theory.

• Most such known solutions are of traceless Ricci and Petrov type N with a constant Ricci scalar.
• Thus we assume the Ricci scalar to be constant which leads to a substantial simplification of the field equations.
• We prove that a vacuum solution to quadratic gravity with traceless Ricci tensor of type N and aligned Weyl tensor of any Petrov type is necessarily a Kundt spacetime.