Speaker
Description
Conformally related black hole metrics have been reported to exhibit both conformal factor dependent and independent quasinormal mode (QNM) spectra. We show that these two outcomes correspond to different boundary value problems and resolve the apparent discrepancy in four dimensions. We reduce the Bach perturbation equations to two coupled radial equations of second order. For the Schwarzschild seed metric, the Bach spectrum consists of Regge-Wheeler and spin-1 branches. When the conformal factor and its inverse are nonsingular throughout the black hole exterior, the boundary conditions and the normalization of the time coordinate are preserved, the spectra is invariant under the conformal transformation. The same approach can also reduce perturbation equations of similar form in other theories with higher derivatives to a finite set of radial equations of lower order and test how other symmetries are reflected in QNM spectra.