Super-renormalizable Higher-Derivative Quantum Gravity

Understand

In this paper we study perturbatively an extension of the Stelle higher derivative gravity involving an infinite number of derivative terms.

• We know that the usual quadratic action is renormalizable but is not unitary because of the presence of a ghost in the theory (pole with negative residue in the propagator).
• The new theory is instead ghost-free since an entire function (or form factor) is introduced in the model without involving new poles in the propagator.
• The local high derivative theory is recovered expanding the entire functions to the lowest order in the mass scale of the theory.