The Freudenthal gauge symmetry of the black holes of N=2,d=4 supergravity

TL;DR

This paper reveals a local gauge symmetry in N=2, d=4 supergravity black hole solutions, generalizing Freudenthal transformations, which allows rewriting solutions with different variable representations.

Contribution

It introduces a continuous local symmetry extending Freudenthal transformations, showing the non-uniqueness of harmonic function representations of black-hole solutions.

Findings

Identifies a local gauge symmetry in supergravity black holes.

Demonstrates the symmetry's role in rewriting solution variables.

Extends discrete Freudenthal transformations to a continuous local form.

Abstract

We show that the representation of black-hole solutions in terms of the variables H^M which are harmonic functions in the supersymmetric case is non-unique due to the existence of a local symmetry in the effective action. This symmetry is a continuous (and local) generalization of the discrete Freudenthal transformations initially introduced for the black-hole charges and can be used to rewrite the physical fields of a solution in terms of entirely different-looking functions.