Matter scattering in $R_{\mu \nu}^2$ gravity and unitarity

Understand

We investigate the ultraviolet (UV) behavior of two-scalar elastic scattering with graviton exchanges in higher curvature gravity theory.

• In the Einstein gravity, matter scattering is shown not to satisfy tree unitarity at high energy.
• Among a few possible directions to cure unitarity (i.e.
• UV completion of Einstein gravity), string theory, modified gravity, inclusion of high-mass/high-spin states, we take $R_{\mu\nu}^2$ gravity coupled to matter.