Form Factors in Quantum Gravity - contrasting non-local, ghost-free gravity and Asymptotic Safety

TL;DR

This paper reviews the role of form factors in quantum gravity, focusing on non-local, ghost-free gravity and asymptotic safety, and introduces a scalar toy model showing potential compatibility with causal graviton propagation.

Contribution

It provides a comparative analysis of form factors in different quantum gravity approaches and introduces a toy model illustrating Lorentzian asymptotic safety's compatibility with causality.

Findings

Form factors are crucial in organizing gravitational dynamics.

Non-local, ghost-free gravity and asymptotic safety can be related through form factors.

A scalar toy model shows Lorentzian asymptotic safety may allow causal graviton propagation.

Abstract

Form factors constitute the key building block when organising the gravitational dynamics in terms of a curvature expansion. They generalise the concept of momentum-dependent couplings to curved spacetime. Moreover, they may capture modifications of the gravitational interactions at high energy scales in a non-perturbative way. We briefly review the role of form factors in various quantum gravity programmes with special emphasis on non-local, ghost-free gravity and asymptotically safe gravity. In this context, we introduce a quantum gravity motivated scalar toy model, which demonstrates that Lorentzian asymptotic safety may be compatible with the causal propagation of gravitons.