Quantum gravity: a fluctuating point of view

TL;DR

This paper reviews the asymptotic safety scenario for quantum gravity using a functional renormalisation group approach, focusing on the existence of a safe ultraviolet fixed point and its implications for gravity and matter systems.

Contribution

It provides a comprehensive review of the current state of asymptotic safety in quantum gravity, including new insights into fixed points, stability, and the role of matter fields.

Findings

Existence of an asymptotically safe ultraviolet fixed point.

Gravity fluctuations dominate in minimally coupled gravity-matter systems.

Full ultraviolet-infrared trajectories connect quantum and classical gravity regimes.

Abstract

In this contribution, we discuss the asymptotic safety scenario for quantum gravity with a functional renormalisation group approach that disentangles dynamical metric fluctuations from the background metric. We review the state of the art in pure gravity and general gravity-matter systems. This includes the discussion of results on the existence and properties of the asymptotically safe ultraviolet fixed point, full ultraviolet-infrared trajectories with classical gravity in the infrared, and the curvature dependence of couplings also in gravity-matter systems. The results in gravity-matter systems concern the ultraviolet stability of the fixed point and the dominance of gravity fluctuations in minimally coupled gravity-matter systems. Furthermore, we discuss important physics properties such as locality of the theory, diffeomorphism invariance, background independence, unitarity, and access to observables, as well as open challenges.