Superradiance And Stationary Resonances In The Kerr-Sen Black Hole

Superstring theory springing up in recent years is still the only known self-consistent theory which can quantize the gravity and unify the gravity, the electromagnetic interac-tion, the weak interaction and the strong interaction. This theory can explain the cosmic genesis and evolution, and figure out the problems of modern physics. In terms of the dilaton spacetimes in string theory, it has qualitatively different properties from those appearing in general relativity because of the appearance of dilaton. So there have been many investigations concerning the spacetimes of dilaton black hole.In this paper we investigated the superradiance effect of the Kerr-Sen black hole, and proved the superradiance instability of the Kerr-Sen black hole against the low fre-quency charged massive scalar field perturbation. In the case of near-extremal Kerr-Sen black hole, we solved the Klein-Gordon equation analytically by employing the matched asymptotic expansion method, and derived an analytical expression of stationary reso-nances of the charged massive scalar field. At the same time, we numerically scanned the parameter space of the Kerr-Sen black hole by employing the shooting method and got the scalar cloud existence line which depends on the spacetime and the parameters of the perturbation field. We found that the scalar clouds exist for the smaller values of background angular velocity if the values of background charge, field charge or quan-tum number are larger, which shows that the influence of the different parameters on the stationary bound-state resonances of the charged massive scalar filed in the Kerr-Sen background.