# Non-Einsteinian Black Holes in Generic 3D Gravity Theories

## TL;DR

This paper discovers new universal non-Einsteinian black hole solutions in three-dimensional higher derivative gravity theories, showing that certain deformations of BTZ black holes can lose or retain their horizons.

## Contribution

It introduces a class of Kerr-Schild type deformations of BTZ black holes that are solutions in all generic higher derivative gravity theories, extending the understanding of black hole solutions beyond Einstein gravity.

## Key findings

- Deformed non-extremal BTZ black holes lose their horizons.
- Deformed extremal BTZ black holes remain as black holes.
- New universal solutions are valid across all generic higher derivative theories.

## Abstract

The Ba\~nados-Teitelboim-Zanelli (BTZ) black hole metric solves the three-dimensional Einstein's theory with a negative cosmological constant as well as all the generic higher derivative gravity theories based on the metric; as such it is a universal solution. Here, we find, in all generic higher derivative gravity theories, new universal non-Einsteinian solutions obtained as Kerr-Schild type deformations of the BTZ black hole. Among these, the deformed non-extremal BTZ black hole loses its event horizon while the deformed extremal one remains intact as a black hole in any generic gravity theory.