Unitarity and Different Phases of the Extended New Massive Gravity

TL;DR

This paper investigates the extended New Massive Gravity theory, analyzing its unitarity and phase structure through tree-level scattering amplitudes on symmetric backgrounds, identifying ghost-free parameter regions and different phases.

Contribution

It provides a detailed analysis of the parameter space and phase structure of the extended New Massive Gravity with curvature cubed terms using scattering amplitudes.

Findings

Identification of ghost-free parameter regions.

Characterization of different phases of the model.

Analysis of unitarity conditions in the extended gravity theory.

Abstract

We study the New Massive Gravity extended by the curvature cubed invariant and the Cosmological Constant using the tree-level scattering amplitudes on a maximally symmetric space-time. We identify the parameter space, consisting of the ratio between C.C. and graviton mass squared and the relative coupling strength between curvature squared and cubed invariants, for which the massive spin-2 is a ghost. Different phases of this model are also discussed.