Spin-dependent persistence of the loop-cut cancellation

Establish whether the cancellation between the one-loop soft factor and the double-soft KMOC cut persists for spinning black-hole mergers, thereby extending the logarithmic low-frequency waveform to mergers producing a spinning black hole.

Background

The paper explicitly evaluates the next-to-leading-order waveform only in the spin-independent sector. At this order, additional logarithms appearing in the quantum one-loop soft factor cancel against the double-soft region of the one-graviton cut, leaving the classical logarithmic tail. The authors explain that their coherent-spin organization should permit a systematic extension in the classical spin, but they leave unresolved whether the crucial cancellation survives when the merger and remnant carry spin.

References

Since the decomposition W_soft remains valid to all orders in the classical spin, an immediate open question is whether the cancellation in eq:cancellation persists in the presence of spin.

— An Effective $S$-Matrix Approach to Low-Frequency Waveforms from Black Hole Mergers  (2609.10329 - Aoki et al., 9 Sep 2026) in Section 7, “Conclusions and outlook,” third outlook paragraph