Minimal Massive 3D Gravity Unitarity Redux

TL;DR

This paper analyzes the unitarity conditions of Minimal Massive Gravity in 3D, identifying parameter regions that ensure consistency, and explores its potential for flat-space holography, revealing complex deformation behaviors.

Contribution

It extends and simplifies the unitarity analysis of MMG, clarifying the parameter space for consistent theories and initiating the study of flat-space holography for MMG.

Findings

Unitarity constrains MMG parameters to a connected region.

Flat-space limit of MMG is a non-linear deformation of 3D conformal gravity.

Linearisation instability is present in the flat-space limit.

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.