# Universal black hole stability in four dimensions

## TL;DR

This paper demonstrates that in four-dimensional gravity theories with higher-curvature terms, black holes become stable below a certain mass, exhibiting universal thermodynamic properties and infinite lifetimes for small black holes.

## Contribution

It proves black hole stability in a broad class of ghost-free higher-curvature theories, extending the understanding of black hole thermodynamics and stability.

## Key findings

- Small black holes have infinite lifetimes.
- Black holes exhibit universal thermodynamic behavior.
- Stability is achieved below a certain mass in these theories.

## Abstract

We show that four-dimensional black holes become stable below certain mass when the Einstein-Hilbert action is supplemented with higher-curvature terms. We prove this to be the case for an infinite family of ghost-free theories involving terms of arbitrarily high order in curvature. The new black holes, which are non-hairy generalizations of Schwarzschild's solution, present a universal thermodynamic behavior for general values of the higher-order couplings. In particular, small black holes have infinite lifetimes. When the evaporation process makes the semiclassical approximation break down (something that occurs after a time which is usually infinite for all practical purposes), the resulting object retains a huge entropy, in stark contrast with Schwarzschild's case.