Gravitational "seesaw" and light bending in higher-derivative gravity

TL;DR

This paper investigates higher-derivative gravity theories, focusing on photon scattering and a gravitational seesaw mechanism, revealing that such theories shift massive modes to higher energies, complicating experimental detection.

Contribution

It introduces an analysis of photon scattering in sixth-derivative gravity and explores a gravitational seesaw mechanism affecting observable signatures.

Findings

The seesaw mechanism shifts heavy masses to the UV region.

Photon scattering shows signatures of higher derivatives.

Detection of higher derivatives remains experimentally challenging.

Abstract

Local gravitational theories with more than four derivatives have remarkable quantum properties, e.g., they are super-renormalizable and may be unitary in the Lee-Wick sense. Therefore, it is important to explore also the IR limit of these theories and identify observable signatures of the higher derivatives. In the present work we study the scattering of a photon by a classical external gravitational field in the sixth-derivative model whose propagator contains only real, simple poles. Also, we discuss the possibility of a gravitational seesaw-like mechanism, which could allow the make up of a relatively small physical mass from the huge massive parameters of the action. If possible, this mechanism would be a way out of the Planck suppression, affecting the gravitational deflection of low energy photons. It turns out that the mechanism which actually occurs works only to shift heavier masses to the further UV region. This fact may be favourable for protecting the theory from instabilities, but makes experimental detection of higher derivatives more difficult.