Scattering of axial gravitational wave pulses by monopole black holes and QNMs: a semianalytic approach

We study scattering of short Gaussian pulses of axial gravitational waves by a spherically symmetric black hole that has swallowed one or more global monopoles. We qualitatively show how the response of the black hole to the impinging pulses depends both on the number of monopoles the black hole has swallowed and on the symmetry breaking scale of the model which gave rise to the monopoles. We use semianalytical methods to determine the corresponding quasinormal modes that get excited by the impinging pulses and that get imprinted in the black hole's response to the pulses. When generalized to the case of rotating black holes, such modes are also expected to show up in various other dynamical processes such as the ringdown phase of a binary black hole merger in case at least one of the companion black holes of the binary has swallowed one or more global monopoles. (paper)