# LIGO Seminar

Speaker: Keefe Mitman

**High Precision Ringdown Modeling: Multimode Fits and BMS Frames**

Quasi-normal mode (QNM) modeling is an invaluable tool for studying strong gravity, characterizing remnant black holes, and testing general relativity. To date, most studies have focused on the dominant (2,2) mode, and have fit to typical strain waveforms from numerical relativity. But, as gravitational wave observatories become more sensitive, they will be able to resolve higher-order modes. Consequently, multimode fits will prove to be critically important, and in turn will require a more thorough treatment of the asymptotic frame at future null infinity. In this talk, I will present a method for systematically fitting a QNM model containing many modes to a numerical waveform produced using Cauchy-characteristic exaction, which is known to exhibit memory effects. By using multimode fitting as opposed to only fitting the (2, \pm 2, n) modes, we find that we can improve the all-modes mismatch by a factor of roughly 10^{5}. Apart from this, I will also address a critical point that has been overlooked in the literature: the importance of matching the Bondi-van der Burg-Metzner-Sachs (BMS) frame of the numerical waveform to that of the QNM model. By mapping the numerical waveforms to a frame known as the super rest frame, we show that we can improve the all-mode strain mismatch by a factor of roughly 10^{5} compared to the mismatch obtained when using a strain waveform whose BMS frame is not fixed.

Zoom link: https://caltech.zoom.us/j/82072539167