Superradiation And Stability Of A Class Of Spherically Symmetric Charged Black Holes In Four-dimensional Normalized Lovelock Gravity

Lovelock’s theory of gravity is one of the maximum extensions of Einstein’s general relativity,which generates quadratic conserved equations of motion in the higher-dimensional spacetime(D > 4)avoiding the introduction of ghost.However,the equations of motion will reduce to those of general relativity in the four-dimensional spacetime(D = 4).Recently,there exist studies showing that by dimensional regularization,Lovelock gravity may still be different from general relativity in four dimensions.In such a regularized Lovelock gravity,a series of novel black hole solutions which are different from those in general relativity can be obtained in the four-dimensional spacetime.Utilizing the observation of M87* by the Event Horizon Telescope(EHT),one can constrain these black holes.In this thesis,we investigate the stability of a class of charged spherically symmetric black holes under scalar perturbations in the regularized Lovelock gravity.Firstly,the parameter space of the black holes under investigation are constrained according to the size of the M87* shadow.Secondly,the superradiance amplification of the massless charged scalar field is calculated.Finally,the eigenfrequencies of quasinormal modes of the massless charged scalar field and the quasibound states of the massive charged scalar field are obtained by the spectral method.These results indicate that the charged spherically symmetric black holes in Lovelock gravity studied in this thesis is stable under the perturbation of an external scalar field,and there is no superradiance instability.