Minimal Massive 3D Gravity Unitarity Redux

Abstract: A geometrical analysis of the bulk and anti-de Sitter boundary unitarity conditions of 3D "Minimal Massive Gravity" (MMG) (which evades the "bulk/boundary clash" of Topologically Massive Gravity) is used to extend and simplify previous results, showing that unitarity selects, up to equivalence, a connected region in parameter space. We also initiate the study of flat-space holography for MMG. Its relevant flat space limit is a deformation of 3D conformal gravity; the deformation is both non-linear and non-conformal, implying a linearisation instability.