Some remarks on high derivative quantum gravity

TL;DR

This paper investigates the ultraviolet behavior, divergences, and unitarity issues of high derivative quantum gravity, exploring its implications for multi-scale gravity and the stability of matter theories at high energies.

Contribution

It provides a detailed analysis of divergences, gauge independence, and unitarity in high derivative quantum gravity, and discusses the potential for multi-scale gravity models.

Findings

Ultraviolet divergences are gauge and reparametrization independent.

Cosmological counterterms can vanish under specific parameters.

Asymptotic freedom of matter theories remains stable under quantum gravity corrections.

Abstract

We analyze the perturbative implications of the most general high derivative approach to quantum gravity based on a diffeomorphism invariant local action. In particular, we consider the super-renormalizable case with a large number of metric derivatives in the action. The structure of ultraviolet divergences is analyzed in some detail. We show that they are independent of the gauge fixing condition and the choice of field reparametrization. The cosmological counterterm is shown to vanish under certain parameter conditions. We elaborate on the unitarity problem of high derivative approaches and the distribution of masses of unphysical ghosts. We also discuss the properties of the low energy regime and explore the possibility of having a multi-scale gravity with different scaling regimes compatible with Einstein gravity at low energies. Finally, we show that the ultraviolet scaling of matter theories is not affected by the quantum corrections of high derivative gravity. As a consequence, asymptotic freedom is stable under those quantum gravity corrections.