  We study a novel class of higher derivative theories for interacting massless
gravitons in Minkowski spacetime. These theories were first discussed by Wald
decades ago, and are characterized by scattering amplitudes essentially
different from general relativity and many of its modifications. We discuss
various aspects of these higher derivative theories, including the Lagrangian
construction, violation of asymptotic causality, scattering amplitudes,
non-renormalization, and possible implications on emergent gravitons from
condensed matter systems.
