Uniqueness of the Axionic Kerr Black Hole
  Under the axisymmetry and under the invarance of simultaneous inversion of time and azimuthal angle, we show that the axionic Kerr black hole is the ${\it unique}$ stationary solution of the minimal coupling theory of gravity and the Kalb-Ramond field, which has a regular event horizon, is asymptotically flat and has a finite axion field strength at event horizon. 
Rue-Ron Hsu, Green Huang and Wei-Fu Lin