Importance of mirror modes in binary black hole ringdown waveform
Arnab Dhani
Abstract
The postmerger signal in binary black hole merger is described by linear, black hole perturbation theory. Historically, this has been modeled using the dominant positive-oscillation frequency (corotating), fundamental mode. Recently, there has been a renewed effort in modeling the postmerger waveform using higher, positive-oscillation frequency overtones in an attempt to achieve greater accuracy in describing the waveform at earlier times using linear perturbation theory. It has been shown that the inclusion of higher overtones can shift the linear regime to the peak of $(l,m)=(2,2)$ spherical harmonic mode. In this work, we show that the inclusion of negative-oscillation frequency (counterrotating) modes, called ``mirror'' modes, extends the validity of linear perturbation theory to even earlier times, with far lower systematic uncertainties in the model in recovering remnant parameters at these early times. A good description of the signal at early times also enables for a greater signal-to-noise ratio to be accumulated in the ringdown phase, thereby allowing for a more accurate measurement of remnant parameters and tests of general relativity.