On the gravitational seesaw in higher-derivative gravity

TL;DR

This paper investigates whether a gravitational seesaw mechanism in higher-derivative gravity theories can produce detectable light particles, concluding that adding more derivatives does not significantly lower the lightest mass, complicating experimental detection.

Contribution

It analyzes the feasibility of a gravitational seesaw mechanism in higher-derivative gravity theories and finds that increasing derivatives does not reduce the lightest mass as hoped.

Findings

Seesaw mechanism does not significantly lower the lightest mass in higher-derivative theories.

Adding more derivatives increases heavier masses but leaves the lightest ghost mass relatively unchanged.

Experimental detection of higher derivatives remains challenging due to mass hierarchy constraints.

Abstract

Local gravitational theories with more than four derivatives are superrenormalizable, and also may be unitary in the Lee-Wick sense. Thus, it is relevant to study the low-energy properties of these theories, especially to identify observables which might be useful for experimental detection of higher derivatives. Using an analogy with the neutrino Physics, we explore the possibility of a gravitational seesaw mechanism, in which several dimensional parameters of the same order of magnitude produce a hierarchy in the masses of propagating particles. Such a mechanism could make a relatively light degree of freedom detectable in low-energy laboratory and astrophysical observations, such as torsion balance experiments and the bending of light. We demonstrate that such a seesaw mechanism in the six- and more-derivative theories is unable to reduce the lightest mass more than in the simplest four-derivative model. Adding more derivatives to the four-derivative action of gravity makes heavier masses even greater, while the lightest massive ghost is not strongly affected. This fact is favorable for protecting the theory from instabilities, but makes the experimental detection of higher derivatives more difficult.