Dissection of a merger-ringdown waveform in the small-mass-ratio limit

Patrick Bourg; Lorenzo Küchler; Benjamin Leather; Kevin Cunningham; Jack Lewis; Adam Pound; Béatrice Bonga; Marc Casals; Rodrigo Panosso Macedo

arXiv · 2609.06861

Dissection of a merger-ringdown waveform in the small-mass-ratio limit

Patrick Bourg·Lorenzo Küchler·Benjamin Leather·Kevin Cunningham·Jack Lewis·Adam Pound·Béatrice Bonga·Marc Casals·Rodrigo Panosso Macedo

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Abstract

Work over the past two decades has unveiled the rich phenomenology of black hole binary mergers and subsequent ringdowns, involving a tapestry of quasinormal modes (QNMs), nonlinearities, tails, transients, and secular effects including gravitational memory. Here we develop a framework for analyzing nonlinear merger-ringdown features in the small-mass-ratio limit, where individual effects can be cleanly isolated. Specializing to the case of a quasicircular, nonspinning black hole binary, we find the waveform sharply divides into a pre-merger extended inspiral phase, a merger phase lasting roughly half a cycle, and a post-merger ringdown dominated by QNMs. We show quadratic QNMs dominate over linear overtones in the ringdown phase for comparable-to-intermediate mass ratios, and we highlight nonlinear effects of gravitational-wave memory, including cubic wave-zone phenomena analogous to horizon absorption effects.

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Patrick Bourg, Lorenzo Küchler, Benjamin Leather, Kevin Cunningham, Jack Lewis, Adam Pound, Béatrice Bonga, Marc Casals, Rodrigo Panosso Macedo. 2026-09-06. Dissection of a merger-ringdown waveform in the small-mass-ratio limit. https://arxiv.org/abs/2609.06861

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