Perturbative $S$-matrix unitarity ($S^{†}S=1$) in $R_{\mu \nu }^2$ gravity

Yugo Abe, Takeo Inami, Keisuke Izumi

We show that in the quadratic curvature theory of gravity, or simply $R_{\mu \nu }^2$ gravity, the tree-level unitariy bound (tree unitarity) is violated in the UV region but an analog…