Chiral limit of fully nonlinear minimal massive gravity

We study 3D anti–de Sitter minimal massive gravity in two regimes: a) at the chiral limit where one of the boundary Brown-Henneaux central charges vanishes and two modes become null and b) in the regime where one of the two charges is much larger than the other. At the chiral point, we go beyond the known free-theory analysis to prove that these modes decouple completely also in the full MMG Lagrangian and field equations. We also use the full action to ascertain if the interacting theory becomes infinitely strongly coupled in the neighborhood of the chiral limit, where the theory is not unitary. We show that this is not the case at tree level but that a strong coupling pathology appears in loops, starting at a loop level determined by the number of external legs in the bulk Feynman diagrams. Finally, we show that there is no strong coupling problem in the second regime where, instead, the two boundary fields and the field propagating in the bulk decouple from one another.