Quasi-normal modes of Schwarzschild–de Sitter black holes

The low-laying frequencies of characteristic quasi-normal modes (QNM) of Schwarzschild-de Sitter (SdS) black holes have been calculated for fields of different spin using the 6th-order WKB approximation and the approximation by the P"oshl-Teller potential. The well-known asymptotic formula for large l is generalized here on a case of the Schwarzchild-de Sitter black hole. In the limit of the near extreme L term the results given by both methods are in a very good agreement, and in this limit fields of different spin decay with the same rate. In addition, the fact that the spectrum of massless Dirac quasi-normal frequencies is the same for opposite chyrality has been numerically proved for SdS background.