The family of metrics corresponding to the plane-fronted gravitational waves with parallel propagation, commonly referred to as the family of pp-wave metrics, is studied in the context of various modified gravitational models in a self-contained and coherent manner by using a variant of the null coframe formulation of Newman and Penrose and the exterior algebra of differential forms on pseudo-Riemannian manifolds.
"pp-waves in modified gravity,"
Turkish Journal of Physics: Vol. 40:
2, Article 1.
Available at: https://journals.tubitak.gov.tr/physics/vol40/iss2/1