The Freudenthal gauge symmetry of the black holes of N=2,d=4   supergravity
  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. 
Pietro Galli, Patrick Meessen and Tomas Ortin
hep-th gr-qc