EFFECT OF COSMIC STRING IN SPHERICALLY SYMMETRIC BLACK HOLE ON THE DIRAC PERTURBATION

The effect of cosmic string on the quasinormal modes (QNMs) of massless Dirac field perturbations were studied in different black hole spacetimes. Quasi-normal mode frequencies of massless Dirac field in Schwarzschild, RN extremal, SdS and near extremal SdS black hole spacetimes with cosmic string are obtained using WKB approximation. Our study shows a clear deviation in QNMs due to presence of cosmic string from those in the absence of string. The influence of cosmic string coded in the form of an increase in the oscillation frequency and damping time of QNMs.