A parametrized quasi-normal mode framework for non-Schwarzschild metrics

In this work we comment in more detail on what happens to the parametrized framework first presented by Cardoso et al. when there are departures from the Schwarzschild background metric, as well as possible deviations in the "dynamics". We treat possible deviations in the background metric with additional coefficients with respect to the original works. The advantages of this reformulation are clear when applied to a parameter estimation problem, since the coefficients are always real, and many of them do not depend on the overtone number and angular momentum of the frequency, thus eventually reducing the total amount of parameters to be inferred.