Quantum Spectrum of Stationary Axisymmetric Einstein--Maxwell Dilaton--Axion Black Hole

The horizon area spectrum of a stationary axisymmetric Einstein--Maxwell Dilaton--Axion (EMDA) black hole is studied by using Gour--Medved’s method. It is found that the quantized area operator can be expressed in terms of two quantum numbers, i.e. A=8πħ(1/2+n+l), where n and l are strictly non-negative integers and related respectively to the mass and angular momentum. The result shows that there is qualitatively a property difference between the quantum spectrum of the EMDA black hole which obtained from string theory and the one of the Kerr--Newman black hole which obtained from general relativity, although both they are characterized by mass, angular momentum and charge.