Spinning Black Hole Scattering at $\mathcal{O}(G^3{S}^2)$: Casimir Terms, Radial Action and Hidden Symmetry

Dogan Akpinar, Fernando Febres Cordero, Manfred Kraus +2

We resolve subtleties in calculating the post-Minkowskian dynamics of binary systems, as a spin expansion, from massive scattering amplitudes of fixed finite spin. In particular, t…