First Look at Quartic-in-Spin Binary Dynamics at Third Post-Minkowskian Order

Author(s): Dogan Akpinar, Fernando Febres Cordero, Manfred Kraus, Alexander Smirnov, and Mao Zeng We compute the conservative and radiation-reaction contributions to classical observables in the gravitational scattering between a spinning and a spinless black hole to the fourth order in spin and third order in the gravitational constant. The conservative results are obtained from two-loop amplit… [Phys. Rev. Lett. 135, 041602] Published Wed Jul 23, 2025