Extremal Black Holes from Homotopy Algebras

TL;DR

This paper develops a homotopy algebra framework to systematically construct and analyze all extremal black hole solutions in Einstein gravity, focusing on their near-horizon geometries and deformations.

Contribution

It introduces a novel homotopy algebra approach to classify extremal black hole deformations using $L_$-algebras and homological perturbation theory.

Findings

Characterizes the moduli space of extremal black hole deformations.

Provides a systematic method to solve deformation equations order by order.

Applies the formalism to extremal Kerr black hole deformations.

Abstract

The uniqueness and rigidity of black holes remain central themes in gravitational research. In this work, we investigate the construction of all extremal black hole solutions to the Einstein equation for a given near-horizon geometry, employing the homotopy algebraic perspective, a powerful and increasingly influential framework in both classical and quantum field theory. Utilising Gau{\ss}ian null coordinates, we recast the deformation problem as an analysis of the homotopy Maurer-Cartan equation associated with an $L_\infty$-algebra. Through homological perturbation theory, we systematically solve this equation order by order in directions transverse to the near-horizon geometry. As a concrete application of this formalism, we examine the deformations of the extremal Kerr horizon. Notably, this homotopy-theoretic approach enables us to characterise the moduli space of deformations by studying only the lowest-order solutions, offering a systematic way to understand the landscape of extremal black hole geometries.