Sifting quantum black holes through the principle of least action

TL;DR

This paper investigates whether quantum gravity can produce regular black holes through an action principle, finding that such solutions require fine-tuning or non-local effects, indicating a fundamental incompatibility with locality.

Contribution

It demonstrates that regular black holes cannot naturally arise from a local action principle in quantum gravity without fine-tuning or non-localities.

Findings

Regular black holes require fine-tuning in the action

Strong infrared non-localities are necessary for such solutions

Locality at large distances conflicts with proposed black hole alternatives

Abstract

We tackle the question of whether regular black holes or other alternatives to the Schwarzschild solution can arise from an action principle in quantum gravity. Focusing on an asymptotic expansion of such solutions and inspecting the corresponding field equations, we demonstrate that their realization within a principle of stationary action would require either fine-tuning, or strong infrared non-localities in the gravitational effective action. This points to an incompatibility between large-distance locality and many of the proposed alternatives to classical black holes.