Breno L. Giacchini

Low-energy effects in a higher-derivative gravity model with real and complex massive poles

The most simple superrenormalizable model of quantum gravity is based on the general local covariant six-derivative action. In addition to graviton such a theory has massive scalar and tensor modes. It was shown recently that in the case when the massive poles emerge in complex conjugate pairs, the theory has also unitary

Classical and tree-level approaches to gravitational deflection in higher-derivative gravity

S

On the gravitational seesaw in higher-derivative gravity

-matrix and hence can be seen as a candidate to be a consistent quantum gravity theory. In the present work we construct the modified Newton potential and explore the gravitational light bending in a general six-derivative theory, including the most interesting case of complex massive poles. In the case of the light deflection the results are obtained within classical and semiclassical approaches.

Experimental limits on the free parameters of higher-derivative gravity

Among the so-called classical tests of general relativity (GR), light bending has been confirmed with an accuracy that increases as times goes by. Here we study the gravitational deflection of photons within the framework of classical and semiclassical higher-derivative gravity (HDG) -- the only version of GR that is known up to now to be renormalizable along with its matter couplings. Since our computations are restricted to scales much below the Planck cut-off we need not be afraid of the massive spin-2 ghost that haunts HDG. An upper bound on the constant related to the

Interesting features of semiclassical gravitational deflection

R^2_{\mu \nu}

Gravitational “seesaw” and light bending in higher-derivative gravity

-sector of the theory is then found by analyzing -- from a classical and semiclassical viewpoint -- the deflection angle of a photon passing by the Sun. This upper limit greatly improves that available in the literature.

Light bending in

Local gravitational theories with more than four derivatives are superrenormalizable. They 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.

F\left[g(\square)R\right]

Fourth-derivative gravity has two free parameters,

extended gravity theories

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Dispersive photon propagation in semiclassical higher-derivative gravity

and