Linear dilaton black holes

TL;DR

This paper introduces new four-dimensional Einstein-Maxwell-dilaton-axion black hole solutions asymptotic to a linear dilaton background, analyzing their properties, stability, and superradiance phenomena.

Contribution

It provides novel rotating and non-rotating black hole solutions in EMDA gravity with detailed analysis of their stability and superradiance effects.

Findings

Rotating solutions exhibit superradiance and classical instability.

Non-rotating black holes are stable under spherical perturbations.

Solutions connect to supersymmetric dilaton-axion configurations in certain limits.

Abstract

We present new solutions to Einstein-Maxwell-dilaton-axion (EMDA) gravity in four dimensions describing black holes which asymptote to the linear dilaton background. In the non-rotating case they can be obtained as the limiting geometry of dilaton black holes. The rotating solutions (possibly endowed with a NUT parameter) are constructed using a generating technique based on the Sp(4,R) duality of the EMDA system. In a certain limit (with no event horizon present) our rotating solutions coincide with supersymmetric Israel-Wilson-Perjes type dilaton-axion solutions. In presence of an event horizon supersymmetry is broken. The temperature of the static black holes is constant, and their mass does not depend on it, so the heat capacity is zero. We investigate geodesics and wave propagation in these spacetimes and find superradiance in the rotating case. Because of the non-asymptotically flat nature of the geometry, certain modes are reflected from infinity, in particular, all superradiant modes are confined. This leads to classical instability of the rotating solutions. The non-rotating linear dilaton black holes are shown to be stable under spherical perturbations.