Spectra, vacua and the unitarity of Lovelock gravity in D-dimensional AdS spacetimes

TL;DR

This paper confirms that Lovelock gravity in D dimensions maintains unitarity with a massless spin-2 excitation around constant curvature vacua, similar to Einstein gravity, with specific parameter constraints ensuring unitarity.

Contribution

It explicitly demonstrates unitarity in Lovelock gravity and derives the effective Newton's constant, providing detailed analysis for cubic Lovelock theory.

Findings

Lovelock gravity has a unitary massless spin-2 mode around vacua.

The propagator reduces to Einstein's form with an effective Newton's constant.

Tree-level unitarity constraints define a wide parameter space for the theory.

Abstract

We explicitly confirm the expectation that generic Lovelock gravity in D dimensions has a unitary massless spin-2 excitation around any one of its constant curvature vacua just like the cosmological Einstein gravity. The propagator of the theory reduces to that of Einstein's gravity, but scattering amplitudes must be computed with an effective Newton's constant which we provide. Tree-level unitarity imposes a single constraint on the parameters of the theory yielding a wide range of unitary region. As an example, we explicitly work out the details of the cubic Lovelock theory.