More on Massive 3D Gravity

TL;DR

This paper investigates static solutions and unitarity properties of three-dimensional New Massive Gravity, revealing unique black hole solutions, conditions for unitarity, and novel phenomena in massless limits.

Contribution

It provides a comprehensive analysis of static solutions in NMG with various parameters, including black holes and unitarity conditions, and uncovers new phenomena in the massless limit.

Findings

Black hole solutions asymptotic to (A)dS vacua found for specific parameters

Unitarity conditions depend on the sign of the cosmological constant

Massless limit of NMG exhibits Maxwell-like equations and novel features

Abstract

We explore the space of static solutions of the recently discovered three-dimensional `New Massive Gravity' (NMG), allowing for either sign of the Einstein-Hilbert term and a cosmological term parametrized by a dimensionless constant $\lambda$. For $\lambda=-1$ we find black hole solutions asymptotic (but not isometric) to the unique (anti) de Sitter vacuum, including extremal black holes that interpolate between this vacuum and (a)dS$_2 \times S^1$. We also investigate unitarity of linearized NMG in (a)dS vacua. We find unitary theories for some dS vacua, but (bulk) unitarity in adS implies negative central charge of the dual CFT, except for $\lambda=3$ where the central charge vanishes and the bulk gravitons are replaced by `massive photons'. A similar phenomenon is found in the massless limit of NMG, for which the linearized equations become equivalent to Maxwell's equations.