Ghost-free infinite derivative gravity

TL;DR

This paper constructs a ghost-free infinite derivative gravity theory that extends quadratic curvature models, unifying massive and massless spin-2 fields, and reduces to general relativity at low energies.

Contribution

It introduces a classically consistent, ghost-free infinite derivative gravitational action in closed form, encompassing interactions of massive and massless spin-2 fields.

Findings

The full action is ghost-free only when all higher derivative terms are included.

At low energies, the theory simplifies to general relativity.

The theory describes a bimetric interaction between massive and massless spin-2 fields.

Abstract

We present the construction of a gravitational action including an infinite series of higher derivative terms. The outcome is a classically consistent completion of a well-studied quadratic curvature theory. The closed form for the full action is ghost-free bimetric theory, describing the interactions of a massive and a massless spin-2 field. At energies much smaller than the spin-2 mass scale, the theory reduces to general relativity. For energies comparable to the spin-2 mass, the higher derivative terms completing the Einstein-Hilbert action capture the effects of the additional massive spin-2 field. The theory is only ghost-free when the full series of higher derivatives is kept.