Perturbations of Black Holes in Einstein-Maxwell-Dilaton-Axion (EMDA) Theories

CN Pope, DO Rohrer, BF Whiting - arXiv preprint arXiv:2508.04589, 2025 - arxiv.org
CN Pope, DO Rohrer, BF Whiting
arXiv preprint arXiv:2508.04589, 2025arxiv.org
We extend our earlier work on the linearised perturbations of static black holes in Einstein-
Maxwell-Dilaton (EMD) theories to the case where the black holes are solutions in an
enlarged theory including also an axion. We study the perturbations in a 3-parameter family
of such EMDA theories. The systems of equations describing the linearised perturbations
can always be separated, but they can only be decoupled when the three parameters are
restricted to a 1-parameter family of EMDA theories, characterised by a parameter $ b $ that …
We extend our earlier work on the linearised perturbations of static black holes in Einstein-Maxwell-Dilaton (EMD) theories to the case where the black holes are solutions in an enlarged theory including also an axion. We study the perturbations in a 3-parameter family of such EMDA theories. The systems of equations describing the linearised perturbations can always be separated, but they can only be decoupled when the three parameters are restricted to a 1-parameter family of EMDA theories, characterised by a parameter that determines the coupling of the axion to the term. In the specific case when , the theory is related to an supergravity. In this one case we find that the perturbations in the axial and the polar sectors are related by a remarkable transformation, which generalises one found by Chandrasekhar for the perturbations of Reissner-Nordstr\"om in Einstein-Maxwell theory. This transformation is of a form found in supersymmetric quantum mechanical models. The existence of such mappings between the axial and polar perturbations appears to correlate with those cases where there is an underlying supergravity supporting the solution, even though the black hole backgrounds are non-extremal and therefore not supersymmetric. We prove the mode stability of the static black hole solutions in the supersymmetric EMDA theory. For other values of the parameter in the EMDA theories that allow decoupling of the modes, we find that one of the radial potentials can be negative outside the horizon if is sufficiently large, raising the possibility of there being perturbative mode instabilities in such a case.
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