A Critique of the Asymptotic Safety Program

Abstract

The present practice of Asymptotic Safety in gravity is in conflict with explicit calculations in low energy quantum gravity. This raises the question of whether the present practice meets the Weinberg condition for Asymptotic Safety. I argue, with examples, that the running of Λ and G found in Asymptotic Safety are not realized in the real world, with reasons which are relatively simple to understand. A comparison/contrast with quadratic gravity is also given, which suggests a few obstacles that must be overcome before the Lorentzian version of the theory is well behaved.I make a suggestion on how a Lorentzian version of Asymptotic Safety could potentially solve these problems. *

Finite Quantum Gravity Amplitudes: No Strings Attached

“…Our construction may serve as a benchmark for a broad range of quantum gravity programs. In particular, it is relevant for the asymptotic safety program [73][74][75][76], where the pole structure introduced in this work is a candidate for the physics generating the renormalization group fixed point at the core of the program.…”

Predictive power of grand unification from quantum gravity

“…This has given rise to compelling evidence for the existence of the Reuter fixed point in four-dimensional Euclidean gravity. A number of important open questions exist, which include the fate of the fixed point in Lorentzian signature, its compatibility with background-independence and the presence of potential tachyonic-or ghost-like instabilities, see [70] for a comprehensive critical appraisal of the state of the art in asymptotically safe quantum gravity, and [71] in particular for a discussion of Lorentzian signature. Most importantly, besides questions of internal consistency, a key challenge for quantum gravity is its consistency with observable phenomenology.…”

Critical Reflections on Asymptotically Safe Gravity

“…Dimensionful couplings have power divergences that are simply subtracted in perturbation theory. In line with these arguments, it has been pointed out in [274,275], that the one-loop corrections to gravity-mediated scattering amplitudes cannot be obtained from applying the RG improvement to Newton's coupling.…”